gitea is your friend

[HF]

We left github just last month and decided to host gitea ourselves, and it was 
an improvement on every single level. Especially because now we could use 
proper hooks.
It has almost the same interface. Every person familiar with github can 
contribute.

And it makes migration as easy as possible. You can mirror github repositories 
and therefor use both at the same time. Or you can allow users to login with 
github.

If you want people to leave github, pointing out that the alternative is 
actually an improvement might be the best way.