Missing Gitlab report/renderer in latest version.

[koenhendriks]

• PHPMD version: 2.12.0
• PHP Version: 8.1
• Installation type: composer
• Operating System / Distribution & Version: macOS Monetery 12.4

According to the documentation on phpmd.org and looking at PR #957 there should be support for gitlab as renderer.

Current Behavior

When latest PHPMD is run it fails to find the gitlab report class with the following error:
Can't find the custom report class: gitlab

Expected Behavior

PHPMD runs successfully and reports a json like output created in #957

Steps To Reproduce:

1. Add latest (2.12.0) PHPMD to project with composer: composer require --dev phpmd/phpmd
2. Run phpmd with any rule using gitlab as reporter: ./vendor/bin/phpmd app gitlab cleancode
3. Phpmd fails with error that it cant find gitlab report class.

./vendor/bin/phpmd app gitlab cleancode
Can't find the custom report class: gitlab

4. (optional) Manually check the vendor/phpmd/phpmd/src/main/php/PHPMD/Renderer directory and see that GitlabRenderer.php file is missing.

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• I have added every step to reproduce the bug.
• If possible I added relevant code examples.
• This issue is about 1 bug and nothing more.
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