Use RESET for GUC test, not reconnect

More limited in what it does, better test.

src/test/regress/expected/multi_extension.out

@@ -100,8 +100,8 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
 (1 row)
 
 -- see incompatible version errors out
+RESET citus.enable_version_checks;
 DROP EXTENSION citus;
-\c
 CREATE EXTENSION citus VERSION '5.0';
 ERROR:  specified version incompatible with loaded Citus library
 DETAIL:  Loaded library requires 6.2, but 5.0 was specified.

src/test/regress/sql/multi_extension.sql

@@ -94,8 +94,8 @@ WHERE pgd.refclassid = 'pg_extension'::regclass AND
 	  pgio.schema    NOT IN ('pg_catalog', 'citus');
 
 -- see incompatible version errors out
+RESET citus.enable_version_checks;
 DROP EXTENSION citus;
-\c
 CREATE EXTENSION citus VERSION '5.0';
 
 -- re-create in newest version