That's not exactly true. You just won't be able to use self-hosted infra to validate GitHub PRs a) using GHA and b) for free.

GitHub still supports e.g. PR checks that originate from other systems. We had PR checks before GHA and it's easy enough to go back to that. Jenkins has some stuff built in or you can make some simple API calls.

It's not as convenient, but it works just fine.

Won't those other systems create a cost that is metered in terms of run-time?