skip_archive should not delete _xcom_archive tables since that was cr…

…eated by migration

tests/utils/test_db_cleanup.py

@@ -277,11 +277,13 @@ def test__cleanup_table(self, table_name, date_add_kwargs, expected_to_delete, e
 
     @pytest.mark.parametrize(
         "skip_archive, expected_archives",
-        [pytest.param(True, 0, id="skip_archive"), pytest.param(False, 1, id="do_archive")],
+        [pytest.param(True, 1, id="skip_archive"), pytest.param(False, 2, id="do_archive")],
     )
     def test__skip_archive(self, skip_archive, expected_archives):
         """
         Verify that running cleanup_table with drops the archives when requested.
+
+        Archived tables from DB migration should be kept when skip_archive is True.
         """
         base_date = pendulum.DateTime(2022, 1, 1, tzinfo=pendulum.timezone("UTC"))
         num_tis = 10