Do not use note.errors for successful quick actions

The following discussion from gitlab-foss!5021 (merged) should be addressed:

• @rymai commented on a discussion: (+4 comments)

  @winh I think we just went with the most boring solution we found which was to use note.errors which we already displayed just above the nite textarea so that was convenient. This is definitely a hack. :)

JSON response for successfully applying a label:

{
  "commands_changes": {},
  "valid": false,
  "errors": { "commands_only": ["Added ~\"critical\" label."] }
}