[PATCH] Auto-register from release branches via a release-* push trigger (#377)

## Summary
- Adds a `release-*` glob to the `push.branches` list in
`Registrator.yml` so version-bumping merges to a maintenance branch
(e.g. `release-0.21`) auto-register, just like merges to
`main`/`master`.
- The reusable Registrator workflow is branch-agnostic and validates the
bump against the pushed commit, so only the local caller's trigger needs
widening.
- The existing `paths: [Project.toml]` guard still applies, so only
version-bumping pushes register; incidental pushes to a release branch
do nothing.

Co-authored-by: ITensorBot <278814285+ITensorBot@users.noreply.github.com>

Author: ITensorBot

.github/workflows/Registrator.yml

@@ -5,6 +5,7 @@ on:
     branches:
       - "master"
       - "main"
+      - "release-*"
     paths:
       - "Project.toml"
   issue_comment: