Fix flaky HoverTest.testEnabledWhenHover() race condition

The testEnabledWhenHover test was failing randomly when trying to retrieve
the hover shell for the second part of the test.

Root cause:
- The test has two parts: first with EnabledPropertyTester.setEnabled(true),
  then with setEnabled(false)
- After the first hover is shown and checked, cleanFileAndEditor() is called
- However, the hover shell from the first part may not be fully disposed
  when the second editor is opened and the second hover is triggered
- This causes getHoverShell() to timeout waiting for the new hover shell

Fix:
- Capture a reference to the first hover shell before calling cleanFileAndEditor()
- After cleanFileAndEditor(), explicitly wait for the first shell to be disposed
  using DisplayHelper.waitForCondition() with a 3000ms timeout
- This ensures the hover state is fully reset before the second part begins

This approach follows the pattern used in other recent flaky test fixes in
this repository (e.g., ProgressContantsTest, ProgressViewTests) which use
condition-based waiting to ensure proper cleanup between test phases.

Fixes #926

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vogella

tests/org.eclipse.ui.genericeditor.tests/src/org/eclipse/ui/genericeditor/tests/HoverTest.java

@@ -33,6 +33,7 @@
 import org.eclipse.swt.custom.StyledText;
 import org.eclipse.swt.widgets.Composite;
 import org.eclipse.swt.widgets.Control;
+import org.eclipse.swt.widgets.Display;
 import org.eclipse.swt.widgets.Event;
 import org.eclipse.swt.widgets.Label;
 import org.eclipse.swt.widgets.Link;
@@ -80,7 +81,13 @@ public void testEnabledWhenHover(TestInfo info) throws Exception {
 		assertNotNull(findControl(shell, StyledText.class, AlrightyHoverProvider.LABEL));
 		assertNull(findControl(shell, StyledText.class, WorldHoverProvider.LABEL));
 
+		// Capture the first shell and its display to wait for disposal
+		Shell firstShell = shell;
+		Display display = firstShell.getDisplay();
 		cleanFileAndEditor();
+		// Wait for the hover shell to be disposed after editor cleanup
+		DisplayHelper.waitForCondition(display, 3000, () -> firstShell.isDisposed());
+
 		EnabledPropertyTester.setEnabled(false);
 		createAndOpenFile("enabledWhen.txt", "bar 'bar'");
 		shell= getHoverShell(info, triggerCompletionAndRetrieveInformationControlManager(), true);