Update yoast/phpunit-polyfills requirement from ^2.0 to ^3.0

Updates the requirements on [yoast/phpunit-polyfills](https://github.com/Yoast/PHPUnit-Polyfills) to permit the latest version.
- [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@2.0.0...3.0.0)

---
updated-dependencies:
- dependency-name: yoast/phpunit-polyfills
  dependency-type: direct:development
...

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

composer.json

@@ -43,7 +43,7 @@
 		"syntatis/coding-standard": "^1.4",
 		"szepeviktor/phpstan-wordpress": "^1.3",
 		"wp-phpunit/wp-phpunit": "^6.6",
-		"yoast/phpunit-polyfills": "^2.0"
+		"yoast/phpunit-polyfills": "^3.0"
 	},
 	"scripts": {
 		"phpcs:fix": "vendor/bin/phpcbf",