Advantages for Github Enterprise is that you get more storage, CI minutes, advanced security features, and premium support. If you don't really need any of those, you can stick with Github Team. Though if you're going to use Gitlab CI, I suggest going with Gitlab instead of Github so you won't have to maintain 2 repositories.
Regarding the advantages that Gitlab CI has over Github, there's a detailed explanation here: https://about.gitlab.com/devops-tools/github-vs-gitlab/ci-missing-github-capabilities/
If you need more minutes for Gitlab CI, you can always use your own Gitlab CI runners instead of the shared runners: https://docs.gitlab.com/runner/register/
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