Bump php-actions/phpunit from 3 to 9

Bumps [php-actions/phpunit](https://github.com/php-actions/phpunit) from 3 to 9.
- [Release notes](https://github.com/php-actions/phpunit/releases)
- [Commits](https://github.com/php-actions/phpunit/compare/v3...v9)

---
updated-dependencies:
- dependency-name: php-actions/phpunit
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/unittests.yml

@@ -18,7 +18,7 @@ jobs:
       - uses: php-actions/composer@v6
       - run: |
           cp ./tests/Includes/Config.yaml ./src/Config/Config.yaml
-      - uses: php-actions/phpunit@v3
+      - uses: php-actions/phpunit@v9
         with:
           bootstrap: src/Vendor/autoload.php
           php_version: ${{ matrix.php_version }}