Fix AsyncoreConnectionTests to check if asyncore present

Before 3.12 asyncore was present all the time.
Now we need to check if it is there.

Author: dkropachev

tests/integration/standard/test_connection.py

@@ -446,6 +446,9 @@ class AsyncoreConnectionTests(ConnectionTests, unittest.TestCase):
     def setUp(self):
         if is_monkey_patched():
             raise unittest.SkipTest("Can't test asyncore with monkey patching")
+        if AsyncoreConnection is None:
+            raise unittest.SkipTest(
+                'asyncore does not appear to be installed properly')
         ConnectionTests.setUp(self)
 
     def clean_global_loop(self):