Bump phpunit/phpunit from 9.5.20 to 9.5.21

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 9.5.20 to 9.5.21.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/main/ChangeLog-9.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/9.5.20...9.5.21)

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

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

composer.json

@@ -59,7 +59,7 @@
     },
     "require-dev": {
         "symfony/stopwatch": "5.4.5",
-        "phpunit/phpunit": "9.5.20",
+        "phpunit/phpunit": "9.5.21",
         "roave/security-advisories": "dev-master"
     }
 }