Bump postcss from 8.2.5 to 8.2.6 (#1233)

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.5 to 8.2.6.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.2.5...8.2.6

)

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