test: fix flaky test-http2-pack-end-stream-flag

Signed-off-by: James M Snell <jasnell@gmail.com>
Fixes: #37639

PR-URL: #37814
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-http2-pack-end-stream-flag.js

@@ -32,12 +32,15 @@ server.on('stream', (stream, headers) => {
 function testRequest(path, targetFrameCount, callback) {
   const obs = new PerformanceObserver(
     common.mustCallAtLeast((list, observer) => {
-      const entry = list.getEntries()[0];
-      if (entry.name !== 'Http2Session') return;
-      if (entry.detail.type !== 'client') return;
-      assert.strictEqual(entry.detail.framesReceived, targetFrameCount);
-      observer.disconnect();
-      callback();
+      const entries = list.getEntries();
+      for (let n = 0; n < entries.length; n++) {
+        const entry = entries[n];
+        if (entry.name !== 'Http2Session') continue;
+        if (entry.detail.type !== 'client') continue;
+        assert.strictEqual(entry.detail.framesReceived, targetFrameCount);
+        observer.disconnect();
+        callback();
+      }
     }));
   obs.observe({ type: 'http2' });
   const client =