This has nothing to do with mining (which isn’t worth doing in the first place, especially on CPUs but even on GPUs it’s crap now).
GitLab has a vendetta against their free users, they don’t want them. The last company I worked for went with GitLab and bought the bronze subscription ($4 per developer per month, had everything we needed). A year later GitLab discontinued the bronze tier, now it’s $20 per developer per month for zero more features we would actually use. So we went back to free tier. Half a year later they limited free tier to 5 people per project, which was a headache yet again.
The company moved to GitHub afterwards, $4 per user per month, same amount of features, no bullshit.
GitLab just tries to get you to pay and could give a shit about free users (or users that wanted a cheaper tier than $20 a month). Now they push you to set a credit card for your account, I’d bet with you in a year tops they’ll limit the free tier even further to either kick you off the platform or force you to the premium tier.