Bump phpunit/phpunit from 8.5.2 to 9.0.1

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.2 to 9.0.1.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-8.5.md)
- [Commits](sebastianbergmann/phpunit@8.5.2...9.0.1)

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

composer.json

@@ -16,7 +16,7 @@
         "symfony/yaml": "^4.1 || ^5.0",
         "doctrine/coding-standard": "^6.0 || ^7.0",
         "vimeo/psalm": "^3.0",
-        "phpunit/phpunit": "^8.0",
+        "phpunit/phpunit": "^8.0 || ^9.0",
         "psalm/plugin-phpunit": "^0.5.5 || ^0.6.0 || ^0.7 || ^0.8 || ^0.9"
     },
     "autoload": {