Bump postcss and @salesforce/sfdx-lwc-jest

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [@salesforce/sfdx-lwc-jest](https://github.com/salesforce/sfdx-lwc-jest). These dependencies need to be updated together.


Updates `postcss` from 8.3.11 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.3.11...8.4.31)

Updates `@salesforce/sfdx-lwc-jest` from 0.13.0 to 3.0.1
- [Release notes](https://github.com/salesforce/sfdx-lwc-jest/releases)
- [Changelog](https://github.com/salesforce/sfdx-lwc-jest/blob/master/CHANGELOG.md)
- [Commits](salesforce/sfdx-lwc-jest@v0.13.0...v3.0.1)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: "@salesforce/sfdx-lwc-jest"
  dependency-type: direct:development
...

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