fix GeoJSONResponse model bug per openapi docs

Author: jkeifer

src/stapi_fastapi/responses.py

@@ -4,6 +4,4 @@
 
 
 class GeoJSONResponse(JSONResponse):
-    def __init__(self, *args, **kwargs) -> None:
-        kwargs["media_type"] = TYPE_GEOJSON
-        super().__init__(*args, **kwargs)
+    media_type = TYPE_GEOJSON