Document Display.test_sleep's false positive problem

As this test has been tagged gtk4-todo, the intention is to make the
test stop false positive results as part of gtk4-todo work.

See #2757
for where the `@Tag`s were added.

Part of #2714

Author: jonahgraham

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Display.java

@@ -1337,6 +1337,12 @@ protected void asyncExec (Runnable runnable) {
 	}
 }
 
+/*
+ * this test false passes on GTK4 when not run in isolation. The test probably
+ * needs some work to ensure it is a valid test, such as making sure that it is
+ * the display.wake that wakes the first display.sleep call. Also checking the
+ * first call to display.sleep does return true.
+ */
 @Tag("gtk4-todo")
 @Test
 public void test_sleep() {