fix: 잘못된 Serializer 사용 수정

Author: MU-Software

app/participant_portal_api/views/file.py

@@ -42,4 +42,4 @@ def upload(self, request: request.Request, *args: tuple, **kwargs: dict) -> resp
         serializer.is_valid(raise_exception=True)
         instance = serializer.save()
 
-        return response.Response(data=PublicFilePortalUploadSerializer(instance).data, status=status.HTTP_201_CREATED)
+        return response.Response(data=PublicFilePortalSerializer(instance).data, status=status.HTTP_201_CREATED)