Syncing the code is the easy and trivial part and your CI job is only solving that. And in my opinion, it's not even that necessary for most projects.

The difficult part is all what's around the code:

* the tickets/PR (including the closed ones)

* the links referencing the project

* the CI setup

* for large projects, the committers permission setup

* if applicable, the push/commit/branch rules

All that will be deeply annoying to migrate on a per project basis, or might get lost.

But that's not even the worst on my opinion. Losing the go-to platform for finding software is (fediverse for software when?).

Syncing is trivial, the CI is the deal. GH actions are the best option still. Neither the FSF nor any other OSS lab didn't come up with a proper CI for us open source maintainers. The CI load also increased massively since.

Setting up own GitLab instance might be a good solution too.