fix: attempting another fix at impersonating service account (#2081)

* Provide an escape hatch for development if the impersonation env
  variable is not set
* Fix default credential fetching

warehouse/oso_dagster/resources/bq_dts.py

@@ -71,17 +71,19 @@ def get_client(self) -> Iterator[DataTransferServiceClient]:
             with setup_gcp_creds(self.gcp_credentials):
                 yield DataTransferServiceClient()
 
-        else:
+        elif impersonate_service_account != "":
             # By default, create an impersonated credential for a service account.
             # This is necessary to create BigQuery DataTransfer jobs
-            credentials = auth.default()
+            credentials, project_id = auth.default()
             target_credentials = impersonated_credentials.Credentials(
                 source_credentials=credentials,
                 target_principal=impersonate_service_account,
-                delegates=[],
                 target_scopes=IMPERSONATE_SCOPES,
-                lifetime=IMPERSONATE_LIFETIME)
+                lifetime=IMPERSONATE_LIFETIME
+            )
             yield DataTransferServiceClient(credentials=target_credentials)
+        else:
+            yield DataTransferServiceClient()
 
     def get_object_to_set_on_execution_context(self) -> Any:
         with self.get_client() as client: