[llvm] [Github] Use standard checkout for ABI test workflows (PR #158468)

[Tom Stellard via llvm-commits]

tstellar wrote:

I think I did it, because it was faster than the checkout action for when you didn't care about the git history.  I'm fine with dropping it, though.  No that we have composite actions, I think we can probably drop or replace everything from the actions repo.

https://github.com/llvm/llvm-project/pull/158468