chore: upgrade Node 24 GitHub Actions

[thinkingfish]

Summary

• upgrade actions/checkout from v4 to v5
• leave artifact and third-party actions unchanged

This action major updates its runtime from Node 20 to Node 24. Self-hosted runners must be v2.327.1 or later.

Validation

• parsed every workflow YAML file
• confirmed no targeted v4 references remain
• confirmed no actions/setup-node or project Node version declarations exist
• inspected the workflow-only diff and ran git diff --check

[brayniac]

Reviewed. actions/checkout@v4 → @v5 (plus actions/cache/restore and save where present), which is the Node 24 migration — Node 20 is deprecated on the runners and already emits a warning on every job in this org.

Mechanical and correct. One thing worth recording, since it was not obvious from the diff.

The workflow rewrite and this bump do not collide

tag-release.yml in the protocol crates was rewritten wholesale a day ago to adopt the pull-request dev bump, and that rewrite kept checkout@v4. A clean merge does not tell you which side of an overlapping edit survived, so I performed the merge locally and looked at the result:

merged tag-release.yml:
  20:      - uses: actions/checkout@v5     <- this PR
  ...
           gh pr create \                  <- the workflow rewrite

Both survive. Git resolved it correctly because the rewrite left that line untouched relative to the base, so only one side had modified it. No action needed — but it was worth confirming rather than assuming, since the alternative would have been silently reverting one of the two.

No concerns. Good to merge.