Bump serverless from 3.20.0 to 3.21.0

Bumps [serverless](https://github.com/serverless/serverless) from 3.20.0 to 3.21.0.
- [Release notes](https://github.com/serverless/serverless/releases)
- [Changelog](https://github.com/serverless/serverless/blob/main/CHANGELOG.md)
- [Commits](serverless/serverless@v3.20.0...v3.21.0)

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

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