build(deps-dev): bump watchfiles from 0.19.0 to 0.21.0

Bumps [watchfiles](https://github.com/samuelcolvin/watchfiles) from 0.19.0 to 0.21.0.
- [Release notes](https://github.com/samuelcolvin/watchfiles/releases)
- [Commits](samuelcolvin/watchfiles@v0.19.0...v0.21.0)

---
updated-dependencies:
- dependency-name: watchfiles
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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