[#25428] YSQL: enable check_for_isn_and_int8_passing_mismatch

Summary:
This YB_TODO had a comment above it: `/* Enable this check when contrib directory is enabled in build_postgres.py */`.

The contrib directory was enabled by D36639 / caa16a6, so it is now
safe to re-enable this check.
Jira: DB-14659

Test Plan: Jenkins

Reviewers: hsunder, fizaa

Reviewed By: hsunder

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D40885

src/postgres/src/bin/pg_upgrade/check.c

@@ -107,10 +107,8 @@ check_and_dump_old_cluster(bool live_check)
 		check_for_prepared_transactions(&old_cluster);
 	check_for_composite_data_type_usage(&old_cluster);
 	check_for_reg_data_type_usage(&old_cluster);
-#ifdef YB_TODO
-	/* Enable this check when contrib directory is enabled in build_postgres.py */
+
 	check_for_isn_and_int8_passing_mismatch(&old_cluster);
-#endif
 
 	/*
 	 * PG 14 changed the function signature of encoding conversion functions.