Home page for the entire suite (in French) with some screenshots: https://lasuite.numerique.gouv.fr/
Code bases are on GitHub and they use English there: https://github.com/suitenumerique/
Dev handbook (in English): https://suitenumerique.gitbook.io/handbook
Not French and I can't say I personally tried deploying any of them, but I've been admiring their efforts from afar for a while now.
For open source code, there is no risk of confidential information being given to the US government (since there is no confidential information), and moving to another forge would be pretty simple if necessary.
Github had enough mindshare that for a small dev operation it was a form of social networking on top of actual code revision control, and one could get the occasional PR worth looking at; this consideration has essentially gone away as the amount of unreviewed vibecoded slop has skyrocketed
I know I'm biased but I'd run my own git server
but you're right that security is of no object here if you're code is OSS in the first place
For any code you are sharing, I think you are underselling the hosting + sharing convenience. Everyone looks for projects on github, it is what people expect. Hosting it yourself requires managing user signups/accounts/permissions/etc.