v0.5.1

Repository tooling 0.5.1

Nothing changes in how your repository works. This patch fixes the maintainer script that gives a
repository its first Standard update workflow, and makes a missing workflow_dispatch trigger
easy to spot.

• Rerunning standards/propose.ts from a checkout still on the update branch no longer closes that
  branch's own pull request. An unchanged run now closes a same-release pull request only when the
  default branch on GitHub already vendors the release.
• A tracking ref left from an update branch GitHub has deleted no longer makes the next push fail.
• When ci.yml has no workflow_dispatch trigger, the Standard update run now says so and fails
  after opening its pull request, instead of stopping with an unexplained error.

This is a patch release, so its update pull request merges itself once Validate passes. It is the
first release to reach repositories through their own Standard update workflow.