Update "labels" wiki page to clarify it's talking about "topics" not labels

This page https://lab.civicrm.org/extensions/extensions-directory/-/wikis/extension-gitlab-labels mentions labels but they are actually "topics" which you set in your extension repo under Settings - General.

Labels in gitlab are just for issues and merge requests.

Gitlab also calls these topics "tags" but that's confusing too because git itself has tags which are a different thing.

I don't have access to edit the wiki page and this repo doesn't seem like it accepts merge requests, so making a ticket here.