chore(pr-sync) - Updated action to run using Node v24

[fearphage]

• Added Node v24 to the CI testing matrix
• Updated some core action (actions/*) versions
• Switched action to use node24
  This will get rid of Node v20 deprecation warnings.
• Added some security-related things to the CI workflow (permissions, disabled persist-credentials)

Note

There's an unrelated test that is failing locally that I will fix in a separate PR.

[freben]

These changes look sound in isolation, including the Node 24 runtime change and the CI permission and credential-hardening updates. Before merging, can we consolidate this with #166? Both PRs change pr-sync/action.yml to node24, while #166 updates all of the other remaining node20 custom actions and this PR contains the newer CI improvements.

My preferred outcome would be to fold this PRs CI and security changes into #166, or expand this PR to cover the remaining actions and close #166, rather than merge overlapping migrations independently.

The new Node 20/24 matrix has also not actually run on GitHub yet; only the sync check is present and the fork workflow awaits approval. Please run CI after the PRs are consolidated. I did not find a code-level correctness blocker beyond the overlap and verification gap.