Issue #23715: Fix test_sigtimedwait() of test_eintr

sigtimedwait([], timeout) fails with OSError(EINVAL) on OpenIndiana, wait for a
signal which will never be received instead.

Lib/test/eintrdata/eintr_tester.py

@@ -272,7 +272,7 @@ class SignalEINTRTest(EINTRBaseTest):
                          'need signal.sigtimedwait()')
     def test_sigtimedwait(self):
         t0 = time.monotonic()
-        signal.sigtimedwait([], self.sleep_time)
+        signal.sigtimedwait([signal.SIGUSR1], self.sleep_time)
         dt = time.monotonic() - t0
         self.assertGreaterEqual(dt, self.sleep_time)