github ci jobs with debug runtime for macos

[gretay-js]

Add two new jobs on macos with debug runtime on. Hopefully it'll help us debug the recurring failure in warnings.ml.

[mshinwell]

The runtime4 failure is:

  * frame #0: 0x00000001986ab720 libsystem_kernel.dylib`__pthread_kill + 8
    frame #1: 0x00000001986e3f70 libsystem_pthread.dylib`pthread_kill + 288
    frame #2: 0x00000001985f0908 libsystem_c.dylib`abort + 128
    frame #3: 0x000000010000d31c test_atomic`caml_failed_assert(expr="Is_in_heap(fp)", file_os=<unavailable>, line=681) at misc.c:55:3 [opt]
    frame #4: 0x00000001000155c0 test_atomic`caml_modify(fp=0x000000013f00dff8, val=-1) at memory.c:681:5 [opt]
    frame #5: 0x000000010000d810 test_atomic`caml_atomic_exchange(ref=<unavailable>, v=<unavailable>) at misc.c:278:3 [opt]
    frame #6: 0x0000000100004fc8 test_atomic`camlTest_atomic__entry + 544

[mshinwell]

This is the part of the test that fails:

let () =
  let r = Atomic.make 0 in
  let cur = Atomic.get r in
  ignore (Atomic.set r (cur + 1), Atomic.set r (cur - 1));
  assert (Atomic.get r <> cur)

[mshinwell]

This will be fixed by #3761