I'm not at all a fan of GitHub actions, but come on, Hudson/Jenkins was a nightmare world, GitHub actions is a million times better

That also is/was awful. But it's just another platform like GHA, and the solution to this kind of thing is always the same, should not be surprising, and is boring in the good way. Write automation so that it's not tightly coupled to the platform on the backend. If you can't migrate between platforms then you're eventually going to be unhappy.

If someone is forcing you towards high stakes tight-coupling with no thought whatsoever towards the lock-in, you should get it in writing that "we at ${org} are fully committed to ${vendor} with ${platform}, on ${cloud} using ${tech} come what may, now and forever" and lots of sign off so that everyone knows who to blame when this is inevitably wrong.