[MM-61459] Fix errcheck issues in server/channels/app/plugin_signatur… (#29202)

server/.golangci.yml

@@ -118,7 +118,6 @@ issues:
         channels/app/platform/web_hub.go|\
         channels/app/platform/web_hub_test.go|\
         channels/app/plugin_install.go|\
-        channels/app/plugin_signature.go|\
         channels/app/plugin_signature_test.go|\
         channels/app/plugin_test.go|\
         channels/app/post.go|\