Bump yoast/phpunit-polyfills from 3.0.0 to 3.1.1 (#486)

Bumps [yoast/phpunit-polyfills](https://github.com/Yoast/PHPUnit-Polyfills) from 3.0.0 to 3.1.1.
- [Release notes](https://github.com/Yoast/PHPUnit-Polyfills/releases)
- [Changelog](https://github.com/Yoast/PHPUnit-Polyfills/blob/3.x/CHANGELOG.md)
- [Commits](Yoast/PHPUnit-Polyfills@3.0.0...3.1.1)

---
updated-dependencies:
- dependency-name: yoast/phpunit-polyfills
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]