Bump postcss, autoprefixer and postcss-cli in /website (#7449)

Bumps [postcss](https://github.com/postcss/postcss), [autoprefixer](https://github.com/postcss/autoprefixer) and [postcss-cli](https://github.com/postcss/postcss-cli). These dependencies needed to be updated together.

Updates `postcss` from 8.4.31 to 8.5.10
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.31...8.5.10)

Updates `autoprefixer` from 9.8.5 to 10.5.0
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](postcss/autoprefixer@9.8.5...10.5.0)

Updates `postcss-cli` from 7.1.2 to 11.0.1
- [Release notes](https://github.com/postcss/postcss-cli/releases)
- [Changelog](https://github.com/postcss/postcss-cli/blob/master/CHANGELOG.md)
- [Commits](postcss/postcss-cli@7.1.2...11.0.1)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.10
  dependency-type: direct:development
- dependency-name: autoprefixer
  dependency-version: 10.5.0
  dependency-type: direct:development
- dependency-name: postcss-cli
  dependency-version: 11.0.1
  dependency-type: direct:development
...

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Author: dependabot[bot]