test: actually test the ttywrap portion of getasyncid

Follow-up from https://github.com/nodejs/node/pull/18800

Code that tries to exercise tty fds must be placed in /pseudo-tty/.

CI: https://ci.nodejs.org/job/node-test-pull-request/13290/

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

test, tty