ci: rebase before pushing the docs theme update commit (#883)

## Summary
Add `pull: '--rebase --autostash'` to the `EndBug/add-and-commit` step
in `manual_release_docs.yaml` so the docs-theme commit survives a
concurrent ref update on the default branch.

## Context
Same race that bit `apify/apify-client-js` in [run
25114327598](https://github.com/apify/apify-client-js/actions/runs/25114327598/job/73597522121):

```
remote rejected (cannot lock ref 'refs/heads/master': is at <new> but expected <old>)
```

The bypass logs `remote: Bypassed rule violations for refs/heads/master`
— so it's not permissions, it's just non-fast-forward because something
landed on master between checkout and push.

The sibling `manual_version_docs.yaml` already uses `pull: '--rebase
--autostash'`; this aligns `manual_release_docs.yaml` with it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)