Mark test_itimer as flaky. NFC

See #20125

Author: sbc100

test/test_other.py

@@ -13255,6 +13255,7 @@ def test_signext_lowering(self):
     err = self.run_process(cmd + ['-sMIN_CHROME_VERSION=73'], stderr=subprocess.PIPE).stderr
     self.assertContained('--signext-lowering', err)
 
+  @flaky('https://github.com/emscripten-core/emscripten/issues/20125')
   def test_itimer(self):
     self.do_other_test('test_itimer.c')