Bump yargs-parser and postcss-cli in /site (#3562)

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

Updates `yargs-parser` from 9.0.2 to 20.2.9
- [Release notes](https://github.com/yargs/yargs-parser/releases)
- [Changelog](https://github.com/yargs/yargs-parser/blob/main/CHANGELOG.md)
- [Commits](yargs/yargs-parser@v9.0.2...yargs-parser-v20.2.9)

Updates `postcss-cli` from 5.0.1 to 10.0.0
- [Release notes](https://github.com/postcss/postcss-cli/releases)
- [Changelog](https://github.com/postcss/postcss-cli/blob/master/CHANGELOG.md)
- [Commits](postcss/postcss-cli@v5.0.1...10.0.0)

---
updated-dependencies:
- dependency-name: yargs-parser
  dependency-type: indirect
- dependency-name: postcss-cli
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]