CI: re-enable LLVM tests on macOS #2520
Description
Right now we disabled all LLVM and C tests on macOS because they hang. See #2455.
We need to re-enable them, to ensure that everything works.
It is not clear why they failed, so we need to investigate and fix that. This is quite high priority, to ensure LPython works on macOS properly. Without it we do not know that things still work.