[3.13] gh-119461: Restore the testSocket VSOCK skipUnless removed by PR GH-119465 (GH-129561) (#129564)

gh-119461: Restore the testSocket VSOCK skipUnless removed by PR GH-119465 (GH-129561)

Restore the skipUnless removed by GH-119465.

This test can only pass on virtual machines, not actual machines.

actual machines see:

```
    self.cli.connect((cid, VSOCKPORT))
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
OSError: [Errno 19] No such device
```

Reproduced on (Linux) Ubuntu 24.04.1 running 6.8.0-52-generic.
(cherry picked from commit e1006ce)

Co-authored-by: Gregory P. Smith <[email protected]>

Author: miss-islington

Lib/test/test_socket.py

@@ -521,6 +521,8 @@ def clientTearDown(self):
 @unittest.skipIf(WSL, 'VSOCK does not work on Microsoft WSL')
 @unittest.skipUnless(HAVE_SOCKET_VSOCK,
           'VSOCK sockets required for this test.')
+@unittest.skipUnless(get_cid() != 2,  # VMADDR_CID_HOST
+                     "This test can only be run on a virtual guest.")
 class ThreadedVSOCKSocketStreamTest(unittest.TestCase, ThreadableTest):
 
     def __init__(self, methodName='runTest'):