Bump docker-commons from 1.19 to 1.21
Bump docker-commons from 1.19 to 1.21

Bumps [docker-commons](https://github.com/jenkinsci/docker-commons-plugin) from 1.19 to 1.21.
- [Release notes](https://github.com/jenkinsci/docker-commons-plugin/releases)
- [Changelog](https://github.com/jenkinsci/docker-commons-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jenkinsci/docker-commons-plugin/compare/docker-commons-1.19...docker-commons-1.21)

---
updated-dependencies:
- dependency-name: org.jenkins-ci.plugins:docker-commons
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
jenkinsci/docker-workflow-plugin,jenkinsci/docker-workflow-plugin