Bump clap from 4.1.6 to 4.1.8 in /cmd/pinniped-proxy

Bumps [clap](https://github.com/clap-rs/clap) from 4.1.6 to 4.1.8.
- [Release notes](https://github.com/clap-rs/clap/releases)
- [Changelog](https://github.com/clap-rs/clap/blob/master/CHANGELOG.md)
- [Commits](clap-rs/clap@v4.1.6...v4.1.8)

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

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