Bump matrix-auth from 2.6.5 to 2.6.6 (#5366)

Bumps [matrix-auth](https://github.com/jenkinsci/matrix-auth-plugin) from 2.6.5 to 2.6.6.
- [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-2.6.5...matrix-auth-2.6.6

)

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