Update yoast/phpunit-polyfills requirement in the dev-dependencies group

Updates the requirements on [yoast/phpunit-polyfills](https://github.com/Yoast/PHPUnit-Polyfills) to permit the latest version.

Updates `yoast/phpunit-polyfills` to 4.0.0
- [Release notes](https://github.com/Yoast/PHPUnit-Polyfills/releases)
- [Changelog](https://github.com/Yoast/PHPUnit-Polyfills/blob/4.x/CHANGELOG.md)
- [Commits](Yoast/PHPUnit-Polyfills@2.0.0...4.0.0)

---
updated-dependencies:
- dependency-name: yoast/phpunit-polyfills
  dependency-version: 4.0.0
  dependency-type: direct:development
  dependency-group: dev-dependencies
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

composer.json

@@ -15,7 +15,7 @@
   },
   "require-dev": {
     "phpunit/phpunit": "9.*",
-    "yoast/phpunit-polyfills": "2.*",
+    "yoast/phpunit-polyfills": "4.*",
     "squizlabs/php_codesniffer": "3.*",
     "wp-coding-standards/wpcs": "3.*",
     "phpcsstandards/phpcsextra": "1.*",