Trusted Publishing on PyPI supports Google Cloud and ActiveState as well. It’s not tied to GitHub or GitLab. To my recollection I looked at CircleCI support a while back, and ran into limitations on the claims they exposed.

(It can also be extended to arbitrary third party IdPs, although the benefit of that is dependent on usage. But if you have another CI/CD provider that you’d like to integrate into PyPI, you should definitely flag it on the issue tracker.)