fixed an extra indent in build_manifest()

src/app.py

@@ -249,7 +249,7 @@ def build_manifest(self, request, response):
             entity_type = source.get("entity_type")
             hubmap_id = source.get("hubmap_id")
             if entity_type is None:
-                        return make_response(jsonify("Required field 'entity_type' was not returned by the query. Make sure it has not been excluded"), 400)
+                    return make_response(jsonify("Required field 'entity_type' was not returned by the query. Make sure it has not been excluded"), 400)
             if entity_type.lower() == "dataset":
                 manifest_list.append(f"{hubmap_id} /")
         if not manifest_list: