deps: bump the dependency-updates group with 3 updates

Bumps the dependency-updates group with 3 updates: [postcss-preset-env](https://github.com/csstools/postcss-plugins/tree/HEAD/plugin-packs/postcss-preset-env), [@testing-library/jest-dom](https://github.com/testing-library/jest-dom) and [eslint-plugin-primer-react](https://github.com/primer/eslint-plugin-primer-react).


Updates `postcss-preset-env` from 10.2.4 to 10.3.0
- [Changelog](https://github.com/csstools/postcss-plugins/blob/main/plugin-packs/postcss-preset-env/CHANGELOG.md)
- [Commits](https://github.com/csstools/postcss-plugins/commits/HEAD/plugin-packs/postcss-preset-env)

Updates `@testing-library/jest-dom` from 6.7.0 to 6.8.0
- [Release notes](https://github.com/testing-library/jest-dom/releases)
- [Changelog](https://github.com/testing-library/jest-dom/blob/main/CHANGELOG.md)
- [Commits](testing-library/jest-dom@v6.7.0...v6.8.0)

Updates `eslint-plugin-primer-react` from 8.0.0 to 8.1.0
- [Release notes](https://github.com/primer/eslint-plugin-primer-react/releases)
- [Changelog](https://github.com/primer/eslint-plugin-primer-react/blob/main/CHANGELOG.md)
- [Commits](primer/eslint-plugin-primer-react@v8.0.0...v8.1.0)

---
updated-dependencies:
- dependency-name: postcss-preset-env
  dependency-version: 10.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dependency-updates
- dependency-name: "@testing-library/jest-dom"
  dependency-version: 6.8.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: dependency-updates
- dependency-name: eslint-plugin-primer-react
  dependency-version: 8.1.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: dependency-updates
...

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

Author: dependabot[bot]