[ci] Sync Translations fails while updating its existing pull request

[taliesin-ai]

Reproduction evidence

Scheduled Sync Translations run 30774299881 failed on 2026-08-03 while updating the existing chore/sync-translations pull request branch.

The translation generation step succeeded. peter-evans/create-pull-request@v4 then:

1. detected the existing remote branch and PR (docs: sync translations #5736),
2. force-with-lease updated chore/sync-translations,
3. logged Fetching existing pull request, and
4. failed in Create Pull Request with Cannot read properties of undefined (reading number).

The runner also reports that the Node 20 actions are being forced onto Node 24. The failure is therefore in PR reconciliation, not translation generation.

Scope

Keep this separate from Beta 3 artifact issue #5876. It affects the scheduled documentation synchronization path and leaves the existing translation PR branch updated even though the workflow is red.

Acceptance criteria

• Update or replace the create/update-PR action with a maintained version compatible with the current runner.
• Verify the path where chore/sync-translations and its pull request already exist.
• Preserve safe branch-update behavior and do not create duplicate PRs.
• A scheduled or equivalent test run completes the PR-update step successfully.

No Project 16 membership or release milestone is assigned: this item was discovered during release triage but is not an eligible current-stage Blocker/Required workstream.

[coderabbitai]

🔗 Related PRs

#3747 - [v3] actions improvements & run actions on more branches and in forks [merged]
#5281 - fix(workflows): rewrite unreleased-changelog-trigger.yml [merged]
#5286 - ci: run v3 nightly release only on 3pm UTC schedule [merged]
#5647 - ci: fix runtime publish (tag/Node), commit regenerated runtime back, auto-commit sponsor image [merged]
#5820 - ci(v3): keep @wailsio/runtime in lockstep with the CLI version [merged]

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