build(deps): bump postcss and @angular-devkit/build-angular in /demo

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies need to be updated together. Updates `postcss` from 8.4.24 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@8.4.24...8.4.31) Updates `@angular-devkit/build-angular` from 16.1.1 to 16.2.5 - [Release notes](https://github.com/angular/angular-cli/releases) - [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md) - [Commits](angular/angular-cli@16.1.1...16.2.5) --- updated-dependencies: - dependency-name: postcss dependency-type: indirect - dependency-name: "@angular-devkit/build-angular" dependency-type: direct:development ... Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]