Exception when shutting down server

[Artur-]

Describe the bug
Whenever the server (Jetty) is shut down, the following is reported in the platform build:

java.lang.IllegalStateException: Cannot access state in VaadinSession or UI without locking the session.
    at com.vaadin.flow.server.VaadinSession.checkHasLock (VaadinSession.java:575)
    at com.vaadin.flow.server.VaadinSession.checkHasLock (VaadinSession.java:589)
    at com.vaadin.flow.internal.StateTree.checkHasLock (StateTree.java:432)
    at com.vaadin.flow.internal.StateTree.beforeClientResponse (StateTree.java:362)
    at com.vaadin.flow.component.UI.beforeClientResponse (UI.java:1281)
    at com.vaadin.flow.component.avatar.AvatarGroup.lambda$setClientItems$2f364bb9$2 (AvatarGroup.java:527)
    at com.vaadin.flow.internal.StateNode.runWhenAttached (StateNode.java:895)
    at com.vaadin.flow.component.avatar.AvatarGroup.setClientItems (AvatarGroup.java:526)
    at com.vaadin.flow.component.avatar.AvatarGroup.setItems (AvatarGroup.java:510)
    at com.vaadin.collaborationengine.CollaborationAvatarGroup.refreshItems (CollaborationAvatarGroup.java:248)
    at com.vaadin.collaborationengine.CollaborationAvatarGroup.lambda$setTopic$93c5f580$1 (CollaborationAvatarGroup.java:160)
    at com.vaadin.collaborationengine.PresenceManager.removeRegistration (PresenceManager.java:248)
    at java.util.LinkedHashMap$LinkedValues.forEach (LinkedHashMap.java:655)
    at com.vaadin.collaborationengine.PresenceManager.resetEntries (PresenceManager.java:259)
    at com.vaadin.collaborationengine.PresenceManager.onConnectionDeactivate (PresenceManager.java:194)
    at java.util.Arrays$ArrayList.forEach (Arrays.java:4204)
    at com.vaadin.flow.shared.Registration.lambda$combine$938b0efe$1 (Registration.java:84)
    at com.vaadin.collaborationengine.EventUtil.fireEvents (EventUtil.java:60)
    at com.vaadin.collaborationengine.TopicConnection.deactivate (TopicConnection.java:558)
    at com.vaadin.collaborationengine.TopicConnection.deactivateAndClose (TopicConnection.java:548)
    at com.vaadin.collaborationengine.TopicConnectionRegistration.remove (TopicConnectionRegistration.java:95)
    at com.vaadin.collaborationengine.CollaborationEngine.clearConnections (CollaborationEngine.java:322)
    at com.vaadin.collaborationengine.CollaborationEngine.lambda$configure$19d34419$1 (CollaborationEngine.java:264)
    at com.vaadin.flow.server.VaadinService.lambda$destroy$6 (VaadinService.java:2079)
    at java.util.concurrent.ConcurrentHashMap$KeySetView.forEach (ConcurrentHashMap.java:4709)
    at java.util.Collections$SetFromMap.forEach (Collections.java:5708)
    at com.vaadin.flow.server.VaadinService.destroy (VaadinService.java:2079)
    at com.vaadin.flow.server.VaadinServlet.destroy (VaadinServlet.java:628)
    at org.eclipse.jetty.servlet.ServletHolder.destroyInstance (ServletHolder.java:455)
    at org.eclipse.jetty.servlet.ServletHolder.doStop (ServletHolder.java:432)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.stop (AbstractLifeCycle.java:132)
    at org.eclipse.jetty.servlet.ServletHandler.doStop (ServletHandler.java:282)
    at org.eclipse.jetty.util.component.AbstractLifeCycle.stop (AbstractLifeCycle.java:132)

To Reproduce
Run vaadin-platform-test in https://github.com/vaadin/platform

Expected behavior
Nothing illegal is done during shutdown

Versions
- Vaadin version: 24 beta 5
- Collaboration Engine version: 6.0.0.beta1