[GPCAPIM-395]: Update environment variables for testing

- Added SDS_URL to the test environment variables

Author: DWolfsNHS

gateway-api/src/gateway_api/test_app.py

@@ -100,8 +100,8 @@ def test_start_app_logs_startup_details(self) -> None:
         test_env_vars = {
             "FLASK_HOST": "test_host",
             "FLASK_PORT": "1234",
-            # TODO 395 - work out where this should be set for testing
-            "PDS_URL": "test_pds_url",
+            "PDS_URL": "test_pds_url",  # TODO 395 - work out where this should be
+            "SDS_URL": "test_sds_url",  # TODO 395 - work out where this should be
         }
 
         with ScopedEnvVars(test_env_vars):