Update integrations/server/test_covidcast_endpoints.py

- add default endpoint comment

Co-authored-by: Katie Mazaitis <krivard@cs.cmu.edu>

Author: dshemetov

integrations/server/test_covidcast_endpoints.py

@@ -39,6 +39,7 @@ def _fetch(self, endpoint="/", is_compatibility=False, **params):
         # make the request
         if is_compatibility:
             url = BASE_URL_OLD
+            # only set endpoint if it's not already set
             params.setdefault("endpoint", "covidcast")
             if params.get("source"):
                 params.setdefault("data_source", params.get("source"))