`test_pthread_print_override_modularize` is failing on macOS after node upgrade to v16

Ever since we updated the version of node running on the emscripten-releases builder or (https://chromium-review.googlesource.com/c/emscripten-releases/+/4634060) this test has been failing consistenly, but only on macOS and only on the emscripten-releases waterfall (not on the github CI mac bots).

See https://logs.chromium.org/logs/emscripten-releases/buildbucket/cr-buildbucket/8777589317403048353/+/u/Emscripten_testsuite__other_/stdout

```
FAIL: test_pthread_print_override_modularize (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/common.py", line 227, in decorated
f(self, *args, **kwargs)
File "/opt/s/w/ir/x/w/install/emscripten/test/test_other.py", line 5960, in test_pthread_print_override_modularize
self.assertContained('hello, earth!', output)
File "/opt/s/w/ir/x/w/install/emscripten/test/common.py", line 1112, in assertContained
self.fail("Expected to find '%s' in '%s', diff:\n\n%s\n%s" % (
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: Expected to find 'hello, earth!
' in 'received "loaded" command from terminated worker: 1
received "callHandler" command from terminated worker: 1
', diff:

--- expected
+++ actual
@@ -1 +1,3 @@
-hello, earth!
+received "loaded" command from terminated worker: 1
+received "callHandler" command from terminated worker: 1
+
```

It seems like some kind of race between the thread/program exiting and postMessages being received from the workers.. but I can't seem to reproduce it.