test: fix flaky test-http2-close-while-writing

The test was flaky due to a race condition where `client.close()` would
wait for a graceful shutdown while the server had already destroyed the
session/stream, leading to a timeout.

Changes:
- Replace `client.close()` with `client.destroy()` in the `close`
  event handler of the client stream.

Refs: #33156

Author: Han5991

test/parallel/test-http2-close-while-writing.js

@@ -38,7 +38,7 @@ server.listen(0, common.mustCall(() => {
   });
   client_stream = client.request({ ':method': 'POST' });
   client_stream.on('close', common.mustCall(() => {
-    client.close();
+    client.destroy();
     server.close();
   }));
   client_stream.resume();