[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 e1006ce1ded1b18972888ef057718dba6f2c7edd)

Co-authored-by: Gregory P. Smith <greg@krypto.org>