composer(deps-dev): update phpunit/phpunit requirement

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-9.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/commits/9.5.3)

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

composer.json

@@ -23,7 +23,7 @@
     },
     "require-dev": {
         "orchestra/testbench": "^6.14.0",
-        "phpunit/phpunit": "^8.0|^9.0"
+        "phpunit/phpunit": "^9.5.3"
     },
     "autoload": {
         "psr-4": {