It's good that alternatives exist, but it's way too early to panic or flee. The sky isn't falling, and we have no idea what, if any, changes this will bring.
Gitlab is nice, but I wonder about its ability to handle a huge increase in users if lots of devs switch. They don't have the best track record when it comes to infrastructure. I am sure they'll see a big spike in usage in the coming weeks, so they're in for a real test.
I would have thought this same anti-MS bias among the dev community would have been the case when MS released Visual Studio Code, but everybody seems to love that and use it, so if Github continues to work like it does now, I doubt most projects will migrate.
EDIT: Sourceforge has announced a Github migration tool you might take a look at.
EDIT 2: For reference, here is the more official discussion, including the Godot position: https://github.com/godotengine/godot/issues/19364