Bump phpunit/phpunit from 8.5.21 to 9.5.28

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.21 to 9.5.28.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/main/ChangeLog-8.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/8.5.21...9.5.28)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

composer.json

@@ -14,6 +14,6 @@
 	},
 	"require-dev": {
 		"nextcloud/coding-standard": "^1.0.0",
-		"phpunit/phpunit": "^8"
+		"phpunit/phpunit": "^9"
 	}
 }