test: move stream test to parallel

I don't believe there's a reason test-stream-writable-clear-buffer needs
to be in sequential. Move it to parallel.

PR-URL: https://github.com/nodejs/node/pull/30561


Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>