change(test_postgresql): return value

tests/test_postgresql.py

@@ -229,7 +229,7 @@ def check_psql(db_conn: dict, query: str) -> tuple:
     except subprocess.CalledProcessError as psql_error:
         return False, str(psql_error).rstrip()
 
-    return True, "OK"
+    return True, None
 
 
 def check_replication(primary: dict, standby: dict) -> tuple: