Merge branch 'doc/unregister-deleted-runners' into 'master'

Add information about unregistering runners

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/170552



Merged-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>
Approved-by: Axel von Bertoldi <avonbertoldi@gitlab.com>
Approved-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>
Co-authored-by: Roshni Sarangadharan <rsarangadharan@gitlab.com>

doc/ci/runners/runners_scope.md

@@ -526,6 +526,11 @@ When you delete a project runner, it is permanently deleted from the GitLab inst
 no longer be used by projects. If you want to temporarily stop the runner from accepting
 jobs, you can [pause](#pause-or-resume-a-project-runner) the runner instead.
 
+When you delete a runner, its configuration still exists in the runner host's `config.toml` file.
+If the deleted runner's configuration is still present in this file, the runner host continues to contact GitLab.
+To prevent unnecessary API traffic, you must also
+[unregister the deleted runner](https://docs.gitlab.com/runner/commands/#gitlab-runner-unregister).
+
 1. On the left sidebar, select **Search or go to** and
    find the project where you want to enable the runner.
 1. Select **Settings > CI/CD**.