bpo-37322: ssl test_pha_required_nocert() ignores expected SSLError (GH-14670)

test_ssl.test_pha_required_nocert() now uses
support.catch_threading_exception() to ignore the expected SSLError
in ConnectionHandler of ThreadedEchoServer (it is only raised
sometimes on Windows).

Lib/test/test_ssl.py

@@ -4326,6 +4326,9 @@ class TestPostHandshakeAuth(unittest.TestCase):
         server_context.verify_mode = ssl.CERT_REQUIRED
         client_context.post_handshake_auth = True
 
+        # Ignore expected SSLError in ConnectionHandler of ThreadedEchoServer
+        # (it is only raised sometimes on Windows)
+        with support.catch_threading_exception() as cm:
             server = ThreadedEchoServer(context=server_context, chatty=False)
             with server:
                 with client_context.wrap_socket(socket.socket(),