Fix Python 3.12 SyntaxWarning in orphaned_toast_tables_check.py

Use raw string literal (r""") for SQL query in orphaned_toast_tables_check.py
to avoid SyntaxWarning on Python 3.12.

The query contains `\d` for PostgreSQL regex which Python 3.12 incorrectly
interprets as an invalid escape sequence, causing test failures on Ubuntu 24.04.

See: #1686

Author: tuhaihe

gpMgmt/bin/gpcheckcat_modules/orphaned_toast_tables_check.py

@@ -25,7 +25,7 @@ def __init__(self):
         # pg_depend back to pg_class, and if the table oids don't match and/or
         # one is missing, the TOAST table is considered to be an orphan.
         # Note: Handles toast tables <pg_toast_temp_*> which is created/used by InitTempTableNamespace().
-        self.orphaned_toast_tables_query = """
+        self.orphaned_toast_tables_query = r"""
 SELECT
     gp_segment_id AS content_id,
     toast_table_oid,