Bump phpunit/phpunit from 10.5.58 to 12.4.2 in /tools/phpunit

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 10.5.58 to 12.4.2.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/12.4.2/ChangeLog-12.4.md)
- [Commits](sebastianbergmann/phpunit@10.5.58...12.4.2)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-version: 12.4.2
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

tools/phpunit/composer.json

@@ -3,7 +3,7 @@
   "description": "Aeon PHP Calendar - Tools",
   "require-dev": {
     "php": "~8.2.0 || ~8.3.0 || ~8.4.0",
-    "phpunit/phpunit": "^10.5"
+    "phpunit/phpunit": "^12.4"
   },
   "config": {
     "allow-plugins": false