Gitlab CI: Fix all jobs validation errors

Quick follow-up on this issue:

Since there were not "too" many issues to fix for each job, I was able to create a single merge request and fix all issues in the same ticket.

Created merge request MR!7 above at #2 with all the necessary changes to fix all jobs validation errors:
Fixed the Stylelint, PHPCS and PHPSTAN very quickly, since there were only a single error for each job.

Fixing ESLint took a bit longer, but using the --fix flag with the eslint command, fixed almost all the issues.
Remaining issues could be fixed manually without too much trouble.

Lastly, since all the jobs were passing, the Gitlab CI config was updated to require all of them to pass.

Since the merge request passed all Tests 🟢, I went ahead and merged the changes above at #3.

Marking issue as Fixed for now.

Feel free to let us know if you encounter any issues while using the module or have any questions or concerns on any of the latest code changes, would be glad to reply as soon as possible.
Thanks in advance for your feedback.