Bump browserslist from 4.12.0 to 4.21.3

Bumps [browserslist](https://github.com/browserslist/browserslist) from 4.12.0 to 4.21.3.
- [Release notes](https://github.com/browserslist/browserslist/releases)
- [Changelog](https://github.com/browserslist/browserslist/blob/main/CHANGELOG.md)
- [Commits](https://github.com/browserslist/browserslist/compare/4.12.0...4.21.3

)

---
updated-dependencies:
- dependency-name: browserslist
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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