Bump phpunit/phpunit from 9.6.22 to 11.5.3 in /tools

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 9.6.22 to 11.5.3.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/11.5.3/ChangeLog-11.5.md)
- [Commits](sebastianbergmann/phpunit@9.6.22...11.5.3)

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

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

Author: dependabot[bot]

tools/composer.json

@@ -2,7 +2,7 @@
     "name": "aeon-php/calendar-tools",
     "description": "Aeon PHP Calendar - Tools",
     "require-dev": {
-        "phpunit/phpunit": "^9.5",
+        "phpunit/phpunit": "^11.5",
         "phpstan/phpstan": "^1.1.2",
         "infection/infection": "^0.29.10",
         "phpbench/phpbench": "^1.2.6",