test: refactor and deflake test-tls-sni-server-client

- Run all tests in parallel.
- Move `socket.end()` call to client.
- Use `common.mustCall()` and `common.mustNotCall()`.

Fixes: https://github.com/nodejs/node/issues/27219
Refs: https://github.com/nodejs/node/pull/27300

PR-URL: https://github.com/nodejs/node/pull/27426


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