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: #30561
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

test/sequential/test-stream-writable-clear-buffer.js → test/parallel/test-stream-writable-clear-buffer.js

@@ -13,7 +13,6 @@ class StreamWritable extends Stream.Writable {
   // Refs: https://github.com/nodejs/node/issues/6758
   // We need a timer like on the original issue thread.
   // Otherwise the code will never reach our test case.
-  // This means this should go in the sequential folder.
   _write(chunk, encoding, cb) {
     setImmediate(cb);
   }