Bump bytemuck from 1.20.0 to 1.21.0

Bumps [bytemuck](https://github.com/Lokathor/bytemuck) from 1.20.0 to 1.21.0.
- [Changelog](https://github.com/Lokathor/bytemuck/blob/main/changelog.md)
- [Commits](Lokathor/bytemuck@v1.20.0...v1.21.0)

---
updated-dependencies:
- dependency-name: bytemuck
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]