Merge branch 'admin-settings-appearance-a11y-label-fixes' into 'master'

Admin appearance settings: Fix a11y label violations

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/182253



Merged-by: Olena Horal-Koretska <ohoralkoretska@gitlab.com>
Approved-by: Ian Gloude <igloude@gitlab.com>
Approved-by: Olena Horal-Koretska <ohoralkoretska@gitlab.com>
Co-authored-by: Sascha Eggenberger <seggenberger@gitlab.com>