Skip the asynchronous test on platforms without socket support

Running an asyncio event loop needs a working socket, which is why
test_unittest.test_async_case skips the whole module without one.

Author: serhiy-storchaka

Lib/test/test_support.py

@@ -1269,6 +1269,8 @@ def test_it(self, a):
         self.assertEqual(len(result.failures), 1)
         self.assertEndsWith(result.failures[0][0].id(), 'test_it (a=2)')
 
+    # Running an asyncio event loop needs a working socket.
+    @support.requires_working_socket()
     def test_async(self):
         # An asynchronous test must be awaited: a synchronous wrapper would
         # make it silently not run at all.