Bump stylelint-config-primer from 3.0.1 to 6.0.0

Bumps [stylelint-config-primer](https://github.com/primer/stylelint-config-primer) from 3.0.1 to 6.0.0.
- [Release notes](https://github.com/primer/stylelint-config-primer/releases)
- [Changelog](https://github.com/primer/stylelint-config-primer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/primer/stylelint-config-primer/commits/v6.0.0

)

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