Fix race condition by waiting for TRUE values instead of non-null

After merging the Phaser-based synchronization from PR eclipse-platform#3429, apply the
critical fix: the processEventsUntil condition was checking if
syncWithDisplayAccess and asyncWithDisplayAccess were not null, but the
test expects these values to be TRUE.

If the async operations executed after started=true is set, they would be
set to FALSE (because !isSTARTED() would be false), causing the test to
fail intermittently.

Changed the condition to wait until both values are TRUE using
Boolean.TRUE.equals() instead of just checking for null.

This ensures the workbench only marks itself as started after the async
operations have completed AND set the expected TRUE values, preventing
the flaky test failures reported in eclipse-platform#1517.

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

Co-Authored-By: Claude <[email protected]>

Author: vogella

tests/org.eclipse.ui.tests.harness/src/org/eclipse/ui/tests/harness/util/RCPTestWorkbenchAdvisor.java

@@ -233,8 +233,8 @@ public void postStartup() {
 
 		// Pump the event loop to ensure async runnables execute before marking as started
 		// This prevents the original race condition where async variables might not be set yet
-		// Wait until the variables that should be set during startup are actually set
-		UITestUtil.processEventsUntil(() -> syncWithDisplayAccess != null && asyncWithDisplayAccess != null, 5000);
+		// Wait until the variables that should be set during startup are actually set to TRUE
+		UITestUtil.processEventsUntil(() -> Boolean.TRUE.equals(syncWithDisplayAccess) && Boolean.TRUE.equals(asyncWithDisplayAccess), 5000);
 		// Process any remaining events to allow variables that should NOT be set during startup
 		// to accidentally execute (to detect regression)
 		UITestUtil.processEvents();