GitLab also has CI built-in, called GitLab CI. You simply need to put into place a configuration file .gitlab-ci.yml in your repo's top directory. That's it. Nothing else. You can then review the CI operations by going to the "CI / CD" tab at your GitLab repository. I've been using GitLab CI for a couple of years now after I got pissed off at Github for being bought by Microsoft and quit using them. :-)
It doesn't really matter which code management system you use these days, they will either have CI built-in or have a 3rd party CI tightly integrated. It is the way forward and I wholeheartedly commend it to all.