Template sync fallback PRs must close after a later successful run

Problem

The release workflow could create a fallback PR on template-sync failure, but a later successful release run left that PR open.

That created zombie PRs like templates/release-sync-failure: stale, conflicted, and already superseded by main.

Root cause

The workflow was asymmetric:

• failure path: create templates/release-sync-failure PR
• success path: push synced templates to main

What it did not have was a cleanup step that closed an already-open fallback PR after the success path landed.

Solution

In release.yml, give the successful template push step an id and add a follow-up cleanup step with actions/github-script.

That cleanup step should:

1. run only when template update succeeded and either:
   • no template changes were produced, or
   • template CI succeeded and the synced templates were pushed to main
2. list open pull requests whose head branch is templates/release-sync-failure
3. comment that the PR is being superseded by the successful sync on main
4. close the PR

Why this works

The fallback PR is just a recovery artifact. Once a later run proves the templates synced cleanly to main, that artifact is no longer the source of truth.

Closing it automatically keeps the release queue clean and prevents reviewers from staring at a dead PR that CI has already made irrelevant.

Prevention

Whenever a workflow has:

• a failure branch that opens a fallback PR
• and a later-success branch that can land the same recovery directly on main

it also needs an explicit cleanup branch that closes any older fallback PRs. GitHub will not do that for free just because the later run skipped the PR-creation step.