Bump matrix-auth from 2.6.7 to 2.6.8

Bumps [matrix-auth](https://github.com/jenkinsci/matrix-auth-plugin) from 2.6.7 to 2.6.8.
- [Release notes](https://github.com/jenkinsci/matrix-auth-plugin/releases)
- [Changelog](https://github.com/jenkinsci/matrix-auth-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jenkinsci/matrix-auth-plugin/compare/matrix-auth-2.6.7...matrix-auth-2.6.8

)

---
updated-dependencies:
- dependency-name: org.jenkins-ci.plugins:matrix-auth
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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