build(deps): bump rustix from 0.38.2 to 0.38.31 in /bench_helpers

Bumps [rustix](https://github.com/bytecodealliance/rustix) from 0.38.2 to 0.38.31.
- [Release notes](https://github.com/bytecodealliance/rustix/releases)
- [Commits](bytecodealliance/rustix@v0.38.2...v0.38.31)

---
updated-dependencies:
- dependency-name: rustix
  dependency-type: indirect
...

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