test: fix flaky test-tls-multiple-cas-as-string

The following error is emitted in a nondeterministic way on the server
side socket on macOS:

```
events.js:173
      throw er; // Unhandled 'error' event
      ^

Error: read ECONNRESET
    at TLSWrap.onStreamRead (internal/stream_base_commons.js:183:27)
Emitted 'error' event at:
    at emitErrorNT (internal/streams/destroy.js:91:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:59:3)
    at processTicksAndRejections (internal/process/task_queues.js:84:9)
```

Prevent the error from being emitted by moving the `socket.end()` call
to the client. Also, run tests in parallel and use `common.mustCall()`.

PR-URL: https://github.com/nodejs/node/pull/27569


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>