Fix errcheck issues in server/channels/web/response_writer_wrapper_te… (#28902)

server/.golangci.yml

@@ -255,7 +255,6 @@ issues:
         channels/utils/license_test.go|\
         channels/web/oauth.go|\
         channels/web/oauth_test.go|\
-        channels/web/response_writer_wrapper_test.go|\
         channels/web/saml.go|\
         channels/web/static.go|\
         channels/web/web.go|\