Release tooling: Label merges as "release"

[JReinhold]

Follow-up to #23198

What I did

#23198 introduces the "release" label for release PRs, that also ensures that CI runs are only triggered with ci:* labels.

This PR changes the "merge-only"/"unreleasable" patch releases to also get the "release" label.

This might technically be less correct, but I think that's okay, given this will save on CI runs and are easily filterable anyway if you ever want to use the labels for searching.

How to test

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]