ref: add non-null assertion after guard against query params (#75157)

this should probably use a serializer instead -- but this is the
quickest fix once models are checked

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Author: asottile-sentry

src/sentry/api/endpoints/debug_files.py

@@ -117,6 +117,8 @@ def post(self, request: Request, project) -> Response:
             error_message = f"Missing required fields: {', '.join(missing_fields)}"
             return Response(data={"error": error_message}, status=status.HTTP_400_BAD_REQUEST)
 
+        assert release_name is not None and proguard_uuid is not None
+
         try:
             uuid.UUID(proguard_uuid)
         except ValueError: