Fix unit tests that sometimes failed due timeouts (#10698)

Motivation:

We had two unit tests that sometimes failed due timeouts. After insepecting these I noticed these can be improved to run faster while still do the right validation

Modifications:

- Only submit one task for execution per execute
- Cleanup

Result:

No test failures due timeout

common/src/test/java/io/netty/util/concurrent/GlobalEventExecutorTest.java

@@ -134,34 +134,22 @@ public class GlobalEventExecutorTest {
         //for https://github.com/netty/netty/issues/1614
         //add scheduled task
         TestRunnable t = new TestRunnable(0);
-        ScheduledFuture<?> f = e.schedule(t, 1500, TimeUnit.MILLISECONDS);
+        final ScheduledFuture<?> f = e.schedule(t, 1500, TimeUnit.MILLISECONDS);
-
-        final Runnable doNothing = new Runnable() {
-            @Override
-            public void run() {
-                //NOOP
-            }
-        };
-        final AtomicBoolean stop = new AtomicBoolean(false);
 
         //ensure always has at least one task in taskQueue
         //check if scheduled tasks are triggered
-        try {
+        e.execute(new Runnable() {
-            new Thread(new Runnable() {
             @Override
             public void run() {
-                    while (!stop.get()) {
+                if (!f.isDone()) {
-                        e.execute(doNothing);
+                    e.execute(this);
                 }
             }
-            }).start();
+        });
 
         f.sync();
 
         assertThat(t.ran.get(), is(true));
-        } finally {
-            stop.set(true);
-        }
     }
 
     private static final class TestRunnable implements Runnable {

common/src/test/java/io/netty/util/concurrent/SingleThreadEventExecutorTest.java

@@ -374,34 +374,22 @@ public class SingleThreadEventExecutorTest {
 
         //add scheduled task
         TestRunnable t = new TestRunnable();
-        ScheduledFuture<?> f = executor.schedule(t, 1500, TimeUnit.MILLISECONDS);
+        final ScheduledFuture<?> f = executor.schedule(t, 1500, TimeUnit.MILLISECONDS);
-
-        final Runnable doNothing = new Runnable() {
-            @Override
-            public void run() {
-                //NOOP
-            }
-        };
-        final AtomicBoolean stop = new AtomicBoolean(false);
 
         //ensure always has at least one task in taskQueue
         //check if scheduled tasks are triggered
-        try {
+        executor.execute(new Runnable() {
-            new Thread(new Runnable() {
             @Override
             public void run() {
-                    while (!stop.get()) {
+                if (!f.isDone()) {
-                        executor.execute(doNothing);
+                    executor.execute(this);
                 }
             }
-            }).start();
+        });
 
         f.sync();
 
         assertThat(t.ran.get(), is(true));
-        } finally {
-            stop.set(true);
-        }
     }
 
     private static final class TestRunnable implements Runnable {