Fix flaky multi_mx_insert_select_repartition test (#7331)

https://github.com/citusdata/citus/actions/runs/6745019678/attempts/1#summary-18336188930
```diff
     insert into target_table SELECT a*2 FROM source_table RETURNING a;
-NOTICE:  executing the command locally: SELECT bytes FROM fetch_intermediate_results(ARRAY['repartitioned_results_xxxxx_from_4213582_to_0','repartitioned_results_xxxxx_from_4213584_to_0']::text[],'localhost',57638) bytes
+NOTICE:  executing the command locally: SELECT bytes FROM fetch_intermediate_results(ARRAY['repartitioned_results_3940758121873413_from_4213584_to_0','repartitioned_results_3940758121873413_from_4213582_to_0']::text[],'localhost',57638) bytes
```

The elements in the array passed to `fetch_intermediate_results` are the
same, but in the opposite order than expected.

To fix this flakiness, we can omit the `"SELECT bytes FROM
fetch_intermediate_results..."` line. From the following logs, it is
understandable that the intermediate results have been fetched.

(cherry picked from commit 0dc41ee5a0)

src/test/regress/expected/multi_mx_insert_select_repartition.out

@@ -103,10 +103,11 @@ NOTICE:  executing the command locally: SELECT count(*) AS count FROM multi_mx_i
      4
 (1 row)
 
+    -- we omit the "SELECT bytes FROM fetch_intermediate_results..." line since it is flaky
+    SET LOCAL citus.grep_remote_commands TO '%multi_mx_insert_select_repartition%';
     insert into target_table SELECT a*2 FROM source_table RETURNING a;
 NOTICE:  executing the command locally: SELECT partition_index, 'repartitioned_results_xxxxx_from_4213581_to' || '_' || partition_index::text , rows_written FROM worker_partition_query_result('repartitioned_results_xxxxx_from_4213581_to','SELECT (a OPERATOR(pg_catalog.*) 2) AS a FROM multi_mx_insert_select_repartition.source_table_4213581 source_table WHERE true',0,'hash','{-2147483648,-715827883,715827882}'::text[],'{-715827884,715827881,2147483647}'::text[],true) WHERE rows_written > 0
 NOTICE:  executing the command locally: SELECT partition_index, 'repartitioned_results_xxxxx_from_4213583_to' || '_' || partition_index::text , rows_written FROM worker_partition_query_result('repartitioned_results_xxxxx_from_4213583_to','SELECT (a OPERATOR(pg_catalog.*) 2) AS a FROM multi_mx_insert_select_repartition.source_table_4213583 source_table WHERE true',0,'hash','{-2147483648,-715827883,715827882}'::text[],'{-715827884,715827881,2147483647}'::text[],true) WHERE rows_written > 0
-NOTICE:  executing the command locally: SELECT bytes FROM fetch_intermediate_results(ARRAY['repartitioned_results_xxxxx_from_4213582_to_0','repartitioned_results_xxxxx_from_4213584_to_0']::text[],'localhost',57638) bytes
 NOTICE:  executing the command locally: INSERT INTO multi_mx_insert_select_repartition.target_table_4213585 AS citus_table_alias (a) SELECT intermediate_result.a FROM read_intermediate_results('{repartitioned_results_xxxxx_from_4213581_to_0,repartitioned_results_xxxxx_from_4213582_to_0,repartitioned_results_xxxxx_from_4213584_to_0}'::text[], 'binary'::citus_copy_format) intermediate_result(a integer) RETURNING citus_table_alias.a
 NOTICE:  executing the command locally: INSERT INTO multi_mx_insert_select_repartition.target_table_4213587 AS citus_table_alias (a) SELECT intermediate_result.a FROM read_intermediate_results('{repartitioned_results_xxxxx_from_4213581_to_2}'::text[], 'binary'::citus_copy_format) intermediate_result(a integer) RETURNING citus_table_alias.a
  a

src/test/regress/expected/multi_mx_insert_select_repartition_0.out

@@ -103,10 +103,11 @@ NOTICE:  executing the command locally: SELECT count(*) AS count FROM multi_mx_i
      4
 (1 row)
 
+    -- we omit the "SELECT bytes FROM fetch_intermediate_results..." line since it is flaky
+    SET LOCAL citus.grep_remote_commands TO '%multi_mx_insert_select_repartition%';
     insert into target_table SELECT a*2 FROM source_table RETURNING a;
 NOTICE:  executing the command locally: SELECT partition_index, 'repartitioned_results_xxxxx_from_4213581_to' || '_' || partition_index::text , rows_written FROM worker_partition_query_result('repartitioned_results_xxxxx_from_4213581_to','SELECT (a OPERATOR(pg_catalog.*) 2) AS a FROM multi_mx_insert_select_repartition.source_table_4213581 source_table WHERE true',0,'hash','{-2147483648,-715827883,715827882}'::text[],'{-715827884,715827881,2147483647}'::text[],true) WHERE rows_written > 0
 NOTICE:  executing the command locally: SELECT partition_index, 'repartitioned_results_xxxxx_from_4213583_to' || '_' || partition_index::text , rows_written FROM worker_partition_query_result('repartitioned_results_xxxxx_from_4213583_to','SELECT (a OPERATOR(pg_catalog.*) 2) AS a FROM multi_mx_insert_select_repartition.source_table_4213583 source_table WHERE true',0,'hash','{-2147483648,-715827883,715827882}'::text[],'{-715827884,715827881,2147483647}'::text[],true) WHERE rows_written > 0
-NOTICE:  executing the command locally: SELECT bytes FROM fetch_intermediate_results(ARRAY['repartitioned_results_xxxxx_from_4213582_to_0','repartitioned_results_xxxxx_from_4213584_to_0']::text[],'localhost',57638) bytes
 NOTICE:  executing the command locally: INSERT INTO multi_mx_insert_select_repartition.target_table_4213585 AS citus_table_alias (a) SELECT a FROM read_intermediate_results('{repartitioned_results_xxxxx_from_4213581_to_0,repartitioned_results_xxxxx_from_4213582_to_0,repartitioned_results_xxxxx_from_4213584_to_0}'::text[], 'binary'::citus_copy_format) intermediate_result(a integer) RETURNING citus_table_alias.a
 NOTICE:  executing the command locally: INSERT INTO multi_mx_insert_select_repartition.target_table_4213587 AS citus_table_alias (a) SELECT a FROM read_intermediate_results('{repartitioned_results_xxxxx_from_4213581_to_2}'::text[], 'binary'::citus_copy_format) intermediate_result(a integer) RETURNING citus_table_alias.a
  a

src/test/regress/sql/multi_mx_insert_select_repartition.sql

@@ -55,6 +55,8 @@ SET citus.log_local_commands to on;
 -- INSERT .. SELECT via repartitioning with local execution
 BEGIN;
     select count(*) from source_table WHERE a = 1;
+    -- we omit the "SELECT bytes FROM fetch_intermediate_results..." line since it is flaky
+    SET LOCAL citus.grep_remote_commands TO '%multi_mx_insert_select_repartition%';
     insert into target_table SELECT a*2 FROM source_table RETURNING a;
 ROLLBACK;