Bump phpunit/phpunit from 8.5.14 to 9.5.5

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.14 to 9.5.5.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-8.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/8.5.14...9.5.5)

---
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

@@ -14,7 +14,7 @@
 	"require-dev": {
 		"roave/security-advisories": "dev-master",
 		"christophwurst/nextcloud": "^21@dev",
-		"phpunit/phpunit": "^8",
+		"phpunit/phpunit": "^9",
 		"nextcloud/coding-standard": "^0.5.0",
 		"symfony/event-dispatcher": "^4.0",
 		"vimeo/psalm": "^4.3",