build(deps-dev): bump @firebase/auth-compat from 0.5.16 to 0.5.21

Bumps [@firebase/auth-compat](https://github.com/firebase/firebase-js-sdk/tree/HEAD/packages/auth-compat) from 0.5.16 to 0.5.21.
- [Release notes](https://github.com/firebase/firebase-js-sdk/releases)
- [Changelog](https://github.com/firebase/firebase-js-sdk/blob/main/packages/auth-compat/CHANGELOG.md)
- [Commits](https://github.com/firebase/firebase-js-sdk/commits/@firebase/[email protected]/packages/auth-compat)

---
updated-dependencies:
- dependency-name: "@firebase/auth-compat"
  dependency-version: 0.5.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]