Bump once_cell from 1.21.3 to 1.21.4 in /autorust (#758)

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.21.3 to 1.21.4.
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](matklad/once_cell@v1.21.3...v1.21.4)

---
updated-dependencies:
- dependency-name: once_cell
  dependency-version: 1.21.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]