Bump the development-dependencies group across 1 directory with 3 updates

Bumps the development-dependencies group with 3 updates in the / directory: [@github/markdownlint-github](https://github.com/github/markdownlint-github), [cssnano](https://github.com/cssnano/cssnano) and [postcss](https://github.com/postcss/postcss).


Updates `@github/markdownlint-github` from 0.8.0 to 0.8.2
- [Release notes](https://github.com/github/markdownlint-github/releases)
- [Changelog](https://github.com/github/markdownlint-github/blob/main/CHANGELOG.md)
- [Commits](github/markdownlint-github@v0.8.0...v0.8.2)

Updates `cssnano` from 8.0.1 to 8.0.2
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@8.0.1...cssnano@8.0.2)

Updates `postcss` from 8.5.15 to 8.5.16
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.15...8.5.16)

---
updated-dependencies:
- dependency-name: "@github/markdownlint-github"
  dependency-version: 0.8.2
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: development-dependencies
- dependency-name: cssnano
  dependency-version: 8.0.2
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: development-dependencies
- dependency-name: postcss
  dependency-version: 8.5.16
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: development-dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]