Remove bad comma in endpoint_macros.pyi

Author: dtkav

openapi_python_client/templates/endpoint_macros.pyi

@@ -61,7 +61,7 @@ if {{ property.python_name }} is not None:
 {% else %}
 ) -> Union[
     {% for response in endpoint.responses %}
-    {{ response.return_string() }},
+    {{ response.return_string() }}{{ "," if not loop.last }}
     {% endfor %}
 ]:
 {% endif %}