test: refactor test-gc-tls-external-memory

- Don’t use network connections, we don’t need them and
  they add more native objects into the mix when we care
  about other kinds of native objects.
- Run GC only once every 64 iterations – this cuts down
  running time from 4 s to 400 ms.
- Use `common.mustCall()` for the `connect()` handler.
- Make sure that the TLS sockets do get garbage collected,
  since the test would otherwise also pass if they remain
  alive indefinitely.

PR-URL: https://github.com/nodejs/node/pull/22651


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>