test: add debugging output for flaky test

Add some debugging output for flaky http2 test to try to figure out
what's going on the next time it fails in CI.

Refs: nodejs#31089

test/parallel/test-http2-large-writes-session-memory-leak.js

@@ -37,6 +37,7 @@ server.listen(0, common.mustCall(() => {
   // create new streams.
   let streamsLeft = 50;
   function newStream() {
+    console.log(`streamsLeft: ${streamsLeft}`);
     const stream = client.request({ ':path': '/' });
 
     stream.on('data', () => { });