Rename group::not_owned label with [DEPRECATED]

What does this MR do and why?

This MR renames the ~"group::not_owned" label to ~"group::not_owned [DEPRECATED]" in unsupported group labels, as this label has been renamed to align with this MR's changes.

Related to #1188 (closed)

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run on how to perform dry-runs.

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review