composer(deps-dev): bump phpunit/phpunit from 10.5.15 to 10.5.21

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 10.5.15 to 10.5.21.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/10.5.21/ChangeLog-10.5.md)
- [Commits](sebastianbergmann/phpunit@10.5.15...10.5.21)

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

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -16,7 +16,7 @@
     "require-dev": {
         "ergebnis/composer-normalize": "2.42.0",
         "infection/infection": "0.27.11",
-        "phpunit/phpunit": "10.5.15",
+        "phpunit/phpunit": "10.5.21",
         "psalm/plugin-phpunit": "0.19.0",
         "symplify/easy-coding-standard": "12.1.14",
         "vimeo/psalm": "5.24.0"