fix: Explicitly check the lock when touching pendingJsInvocations (#22783)

Explicitly check the lock when touching pendingJsInvocations
Alos uses proper UI in test: this ensures that the session is available also from the inside and not
only through a Mockito mock.

Related to #22742

Author: Legioth

flow-server/src/main/java/com/vaadin/flow/component/internal/UIInternals.java

@@ -620,6 +620,7 @@ public void addJavaScriptInvocation(
      * @return a list of pending JavaScript invocations
      */
     public List<PendingJavaScriptInvocation> dumpPendingJavaScriptInvocations() {
+        session.checkHasLock();
         pendingTitleUpdateCanceler = null;
 
         if (pendingJsInvocations.isEmpty()) {
@@ -677,6 +678,7 @@ public void execute() {
 
         private void removePendingInvocation(
                 PendingJavaScriptInvocation invocation) {
+            session.checkHasLock();
             UIInternals.this.pendingJsInvocations.remove(invocation);
             if (invocationList.isEmpty() && registration != null) {
                 registration.remove();
@@ -699,6 +701,7 @@ void onInvocationCompleted(PendingJavaScriptInvocation invocation) {
      */
     // Non-private for testing purposes
     Stream<PendingJavaScriptInvocation> getPendingJavaScriptInvocations() {
+        session.checkHasLock();
         return pendingJsInvocations.stream()
                 .filter(invocation -> !invocation.isCanceled());
     }

flow-server/src/test/java/com/vaadin/flow/server/communication/AtmospherePushConnectionTest.java

@@ -42,6 +42,7 @@
 import com.vaadin.flow.component.UI;
 import com.vaadin.flow.server.MockVaadinSession;
 import com.vaadin.flow.server.communication.AtmospherePushConnection.State;
+import com.vaadin.tests.util.MockUI;
 
 /**
  * @author Vaadin Ltd
@@ -67,9 +68,10 @@ public static void stopExecutor() {
 
     @Before
     public void setup() throws Exception {
-        UI ui = Mockito.spy(new UI());
         vaadinSession = new MockVaadinSession();
-        Mockito.when(ui.getSession()).thenReturn(vaadinSession);
+        vaadinSession.lock();
+        UI ui = new MockUI(vaadinSession);
+        vaadinSession.unlock();
         broadcaster = Mockito.mock(Broadcaster.class);
         resource = Mockito.mock(AtmosphereResource.class);
         Mockito.when(resource.getBroadcaster()).thenReturn(broadcaster);