build(deps): bump slab from 0.4.11 to 0.4.12

Bumps [slab](https://github.com/tokio-rs/slab) from 0.4.11 to 0.4.12.
- [Release notes](https://github.com/tokio-rs/slab/releases)
- [Changelog](https://github.com/tokio-rs/slab/blob/master/CHANGELOG.md)
- [Commits](tokio-rs/slab@v0.4.11...v0.4.12)

---
updated-dependencies:
- dependency-name: slab
  dependency-version: 0.4.12
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]