[MM-61458] Fix errcheck issues in server/channels/app/plugin_requests.go (#29121)

server/.golangci.yml

@@ -133,7 +133,6 @@ issues:
         channels/app/plugin_api_tests/manual.test_serve_metrics_plugin/main.go|\
         channels/app/plugin_api_tests/test_update_user_auth_plugin/main.go|\
         channels/app/plugin_install.go|\
-        channels/app/plugin_requests.go|\
         channels/app/plugin_signature.go|\
         channels/app/plugin_signature_test.go|\
         channels/app/plugin_test.go|\