Fix flaky multi_mx_node_metadata.sql test (#7317)

Fixes the flaky test that results in following diff:
```diff
--- /__w/citus/citus/src/test/regress/expected/multi_mx_node_metadata.out.modified	2023-11-01 14:22:12.890476575 +0000
+++ /__w/citus/citus/src/test/regress/results/multi_mx_node_metadata.out.modified	2023-11-01 14:22:12.914476657 +0000
@@ -840,24 +840,26 @@
 (1 row)

 \c :datname - - :master_port
 SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';
   datname
 ------------
  db_to_drop
 (1 row)

 DROP DATABASE db_to_drop;
+ERROR:  database "db_to_drop" is being accessed by other users
 SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';
   datname
 ------------
-(0 rows)
+ db_to_drop
+(1 row)

 -- cleanup
 DROP SEQUENCE sequence CASCADE;
 NOTICE:  drop cascades to default value for column a of table reference_table
```

(cherry picked from commit 9867c5b949)

src/test/regress/citus_tests/run_test.py

@@ -172,6 +172,15 @@ DEPS = {
     ),
     "grant_on_schema_propagation": TestDeps("minimal_schedule"),
     "propagate_extension_commands": TestDeps("minimal_schedule"),
+    "multi_size_queries": TestDeps("base_schedule", ["multi_copy"]),
+    "multi_mx_node_metadata": TestDeps(
+        None,
+        [
+            "multi_extension",
+            "multi_test_helpers",
+            "multi_test_helpers_superuser",
+        ],
+    ),
 }
 
 

src/test/regress/expected/multi_mx_node_metadata.out

@@ -9,7 +9,7 @@ SET citus.shard_count TO 8;
 SET citus.shard_replication_factor TO 1;
 \set VERBOSITY terse
 -- Simulates a readonly node by setting default_transaction_read_only.
-CREATE FUNCTION mark_node_readonly(hostname TEXT, port INTEGER, isreadonly BOOLEAN)
+CREATE OR REPLACE FUNCTION mark_node_readonly(hostname TEXT, port INTEGER, isreadonly BOOLEAN)
     RETURNS TEXT
     LANGUAGE sql
     AS $$
@@ -27,7 +27,7 @@ CREATE OR REPLACE FUNCTION raise_error_in_metadata_sync()
     RETURNS void
     LANGUAGE C STRICT
     AS 'citus';
-CREATE PROCEDURE wait_until_process_count(appname text, target_count int) AS $$
+CREATE OR REPLACE PROCEDURE wait_until_process_count(appname text, target_count int) AS $$
 declare
    counter integer := -1;
 begin
@@ -846,7 +846,22 @@ SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';
  db_to_drop
 (1 row)
 
-DROP DATABASE db_to_drop;
+DO $$
+DECLARE
+    i int := 0;
+BEGIN
+  WHILE NOT (SELECT bool_and(success) from run_command_on_all_nodes('DROP DATABASE IF EXISTS db_to_drop'))
+  LOOP
+    BEGIN
+      i := i + 1;
+      IF i > 5 THEN
+          RAISE EXCEPTION 'DROP DATABASE timed out';
+      END IF;
+      PERFORM pg_sleep(1);
+    END;
+  END LOOP;
+END;
+$$;
 SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';
  datname
 ---------------------------------------------------------------------

src/test/regress/sql/multi_mx_node_metadata.sql

@@ -14,7 +14,7 @@ SET citus.shard_replication_factor TO 1;
 \set VERBOSITY terse
 
 -- Simulates a readonly node by setting default_transaction_read_only.
-CREATE FUNCTION mark_node_readonly(hostname TEXT, port INTEGER, isreadonly BOOLEAN)
+CREATE OR REPLACE FUNCTION mark_node_readonly(hostname TEXT, port INTEGER, isreadonly BOOLEAN)
     RETURNS TEXT
     LANGUAGE sql
     AS $$
@@ -35,7 +35,7 @@ CREATE OR REPLACE FUNCTION raise_error_in_metadata_sync()
     LANGUAGE C STRICT
     AS 'citus';
 
-CREATE PROCEDURE wait_until_process_count(appname text, target_count int) AS $$
+CREATE OR REPLACE PROCEDURE wait_until_process_count(appname text, target_count int) AS $$
 declare
    counter integer := -1;
 begin
@@ -378,7 +378,22 @@ SELECT trigger_metadata_sync();
 
 SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';
 
-DROP DATABASE db_to_drop;
+DO $$
+DECLARE
+    i int := 0;
+BEGIN
+  WHILE NOT (SELECT bool_and(success) from run_command_on_all_nodes('DROP DATABASE IF EXISTS db_to_drop'))
+  LOOP
+    BEGIN
+      i := i + 1;
+      IF i > 5 THEN
+          RAISE EXCEPTION 'DROP DATABASE timed out';
+      END IF;
+      PERFORM pg_sleep(1);
+    END;
+  END LOOP;
+END;
+$$;
 
 SELECT datname FROM pg_stat_activity WHERE application_name LIKE 'Citus Met%';