Fix response_body

[ndtretyak]

References to other Issues or PRs

Have you read the Contributing Guidelines?

Yes

Brief description of what is fixed or changed

#4622 replaced proto.Message with a concrete response type in response_* structs and removed the line that cast proto.Message, since it seemed that we could now access m's fields directly
https://github.com/grpc-ecosystem/grpc-gateway/pull/4622/files#diff-9648d8792ce733c8bbce0d613a620fffdb73cff98a91763507a1984eb520d5feL766

However, if the response type has a field with the same name (e.g., type Response struct {Response string}) it does not work as expected.

[johanbrandhorst]

Oops, nice find! Thank you.

[johanbrandhorst]

Looks like we need to regenerate some bazel files, you can see the steps in CONTRIBUTING.md