test_itimer is flaky on macOS

[sbc100]

e.g.: https://ci.chromium.org/ui/p/emscripten-releases/builders/ci/mac/b8771894894137094721/overview

======================================================================
FAIL: test_itimer (test_other.other)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/s/w/ir/cache/vpython/store/cpython-ste21jq03jlov0apfh16dstb30/contents/lib/python3.8/unittest/case.py", line 60, in testPartExecutor
    yield
  File "/opt/s/w/ir/cache/vpython/store/cpython-ste21jq03jlov0apfh16dstb30/contents/lib/python3.8/unittest/case.py", line 676, in run
    self._callTestMethod(testMethod)
  File "/opt/s/w/ir/cache/vpython/store/cpython-ste21jq03jlov0apfh16dstb30/contents/lib/python3.8/unittest/case.py", line 633, in _callTestMethod
    method()
  File "/opt/s/w/ir/x/w/install/emscripten/test/test_other.py", line 13278, in test_itimer
    self.do_other_test('test_itimer.c')
  File "/opt/s/w/ir/x/w/install/emscripten/test/test_other.py", line 199, in do_other_test
    return self.do_run_in_out_file_test('other', testname, emcc_args=emcc_args, **kwargs)
  File "/opt/s/w/ir/x/w/install/emscripten/test/common.py", line 1497, in do_run_in_out_file_test
    output = self._build_and_run(srcfile, expected, **kwargs)
  File "/opt/s/w/ir/x/w/install/emscripten/test/common.py", line 1535, in _build_and_run
    js_output = self.run_js(js_file, engine, args,
  File "/opt/s/w/ir/x/w/install/emscripten/test/common.py", line 1127, in run_js
    self.fail('JS subprocess failed (%s): %s.  Output:\n%s' % (error.cmd, error.returncode, ret))
  File "/opt/s/w/ir/cache/vpython/store/cpython-ste21jq03jlov0apfh16dstb30/contents/lib/python3.8/unittest/case.py", line 753, in fail
    raise self.failureException(msg)
AssertionError: JS subprocess failed (/opt/s/w/ir/cache/builder/emscripten-releases/node-v16.20.0-darwin-x64/bin/node --stack-trace-limit=50 --trace-uncaught /opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js): 7.  Output:
ms remaining: 999
ms remaining: 640
Received SIGALRM!
ms remaining: 999
ms remaining: 839
Received SIGVTALRM!
ms remaining: 999
ms remaining: 899
Received SIGPROF!
Received SIGALRM!
Received SIGALRM!
Received SIGALRM!
Received SIGALRM!
Received SIGALRM!
Received SIGALRM!
got 6 alarms
Aborted(Assertion failed: got_alarm[which] > NUM_TIMERS - ERROR_MARGIN, at: /opt/s/w/ir/x/w/install/emscripten/test/other/test_itimer.c,90,test_sequence)
/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:129
      throw ex;
      ^

RuntimeError: Aborted(Assertion failed: got_alarm[which] > NUM_TIMERS - ERROR_MARGIN, at: /opt/s/w/ir/x/w/install/emscripten/test/other/test_itimer.c,90,test_sequence)
    at abort (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:674:11)
    at ___assert_fail (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1153:7)
    at wasm://wasm/00010a4a:wasm-function[13]:0xa49
    at wasm://wasm/00010a4a:wasm-function[15]:0xcaf
    at wasm://wasm/00010a4a:wasm-function[16]:0xcdd
    at /opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:723:14
    at callMain (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1660:15)
    at doRun (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1710:23)
    at run (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1725:5)
    at runCaller (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1645:19)
    at removeRunDependency (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:641:7)
    at receiveInstance (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:860:5)
    at receiveInstantiationResult (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:878:5)
Thrown at:
    at abort (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:674:11)
    at ___assert_fail (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1153:7)
    at wasm://wasm/00010a4a:1:2634
    at wasm://wasm/00010a4a:1:3248
    at wasm://wasm/00010a4a:1:3294
    at /opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:723:14
    at callMain (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1660:15)
    at doRun (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1710:23)
    at run (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1725:5)
    at runCaller (/opt/s/w/ir/x/t/emtest_dt8lyrwm/emscripten_test_other_edst00a5/test_itimer.js:1645:19)