Bump postcss and @angular-devkit/build-angular

Bumps [postcss](https://github.com/postcss/postcss) and [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies needed to be updated together.

Updates `postcss` from 8.5.8 to 8.5.12
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.8...8.5.12)

Updates `@angular-devkit/build-angular` from 21.1.5 to 21.2.9
- [Release notes](https://github.com/angular/angular-cli/releases)
- [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md)
- [Commits](angular/angular-cli@v21.1.5...v21.2.9)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.12
  dependency-type: direct:development
- dependency-name: "@angular-devkit/build-angular"
  dependency-version: 21.2.9
  dependency-type: direct:development
...

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Author: dependabot[bot]