chore(deps): bump postcss from 8.2.9 to 8.2.15 (#7383)

Bumps [postcss](https://github.com/postcss/postcss) from 8.2.9 to 8.2.15.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.2.9...8.2.15)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]