[JENKINS-36871] Fix flaky test

 - On machines with fewer cores than my machine, the selector thread may not have processed the interest removal and hence the test can fail randomly for lower spec machines

src/test/java/org/jenkinsci/remoting/protocol/IOHubTest.java

@@ -246,14 +246,18 @@ public void onClosedChannel(ClosedChannelException e) {
 
         // Wait for registration, in other case we get unpredictable timing related results due to late registration
         while (key.get() == null) {
-            Thread.sleep(100);
+            Thread.sleep(10);
         }
 
         Socket client = new Socket();
         client.setSoTimeout(100);
         client.connect(srv.getLocalAddress(), 100);
         assertThat(IOUtils.toString(client.getInputStream()), is("Go away #1"));
         hub.hub().removeInterestAccept(key.get());
+        // wait for the interest accept to be removed
+        while ((key.get().interestOps() & SelectionKey.OP_ACCEPT) != 0) {
+            Thread.sleep(10);
+        }
         client = new Socket();
         client.setSoTimeout(100);
         client.connect(srv.getLocalAddress(), 100);