Bump yew from 0.20.0 to 0.21.0

Bumps [yew](https://github.com/yewstack/yew) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/yewstack/yew/releases)
- [Changelog](https://github.com/yewstack/yew/blob/master/CHANGELOG.md)
- [Commits](yewstack/yew@yew-v0.20.0...yew-v0.21.0)

---
updated-dependencies:
- dependency-name: yew
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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