fix(dash import): Ensure old datasource ids are not referenced in imported charts (#23582)

tests/integration_tests/dashboards/commands_tests.py

@@ -565,6 +565,9 @@ class TestImportDashboardsCommand(SupersetTestCase):
         dataset = chart.table
         assert str(dataset.uuid) == dataset_config["uuid"]
 
+        assert chart.query_context is None
+        assert json.loads(chart.params)["datasource"] == dataset.uid
+
         database = dataset.database
         assert str(database.uuid) == database_config["uuid"]