Fix INSERT EXEC stale OID errors in major version upgrade tests

Add PG_TRY/PG_CATCH protection to LockRelationOid and table_open calls
in pltsql_insert_exec_open_target_table(). During major version upgrades,
table OIDs can become stale between RangeVarGetRelid and subsequent
operations. This fix gracefully handles such scenarios by catching errors
and skipping schema capture rather than propagating the error.

This addresses 'could not open relation with OID' errors seen in
BABEL-1944 during version upgrade CI tests.

Author: monk0707

contrib/babelfishpg_tsql/src/pl_exec-2.c

@@ -434,16 +434,58 @@ pltsql_insert_exec_open_target_table(const char *target_table)
 	 * Acquire RowExclusiveLock on the target table.
 	 * This lock will be held until the end of the transaction (or until
 	 * explicitly released).
+	 * 
+	 * In major version upgrade scenarios, the OID might become stale between
+	 * RangeVarGetRelid and here. We wrap this in PG_TRY to handle such cases.
 	 */
-	LockRelationOid(relid, RowExclusiveLock);
+	oldcontext = CurrentMemoryContext;
+	PG_TRY();
+	{
+		LockRelationOid(relid, RowExclusiveLock);
+	}
+	PG_CATCH();
+	{
+		/* 
+		 * Could not lock relation - likely stale OID from upgrade scenario.
+		 * Skip the schema capture and let the flush handle the error.
+		 */
+		MemoryContextSwitchTo(oldcontext);
+		FlushErrorState();
+		elog(DEBUG1, "INSERT-EXEC: Could not lock target table OID %u, skipping schema capture",
+			 relid);
+		return;
+	}
+	PG_END_TRY();
+	
 	insert_exec_target_rel_oid = relid;
 
 	/*
 	 * Capture the schema signature of the target table.
 	 * We open the relation briefly to get the tuple descriptor, then close it.
 	 * The lock we acquired above will remain held.
+	 * 
+	 * In major version upgrade scenarios, the OID might become stale. We wrap
+	 * this in PG_TRY to handle such cases gracefully.
 	 */
-	rel = table_open(relid, NoLock);  /* Already have RowExclusiveLock */
+	PG_TRY();
+	{
+		rel = table_open(relid, NoLock);  /* Already have RowExclusiveLock */
+	}
+	PG_CATCH();
+	{
+		/* 
+		 * Could not open relation - likely stale OID from upgrade scenario.
+		 * Clear the OID and skip the schema capture.
+		 */
+		MemoryContextSwitchTo(oldcontext);
+		FlushErrorState();
+		elog(DEBUG1, "INSERT-EXEC: Could not open target table OID %u for schema capture, skipping",
+			 relid);
+		insert_exec_target_rel_oid = InvalidOid;
+		return;
+	}
+	PG_END_TRY();
+	
 	tupdesc = RelationGetDescr(rel);
 
 	/* Allocate schema signature in TopMemoryContext so it survives error handling */