Unprotected access in animation handler

The EvaluateClipAnimatorJob calls Handler::setClipAnimatorRunning, which modifies the m_runningClipAnimators variable (https://codebrowser.dev/qt6/qt3d/src/animation/backend/handler.cpp.html#90). A scene with multiple clip animators will create multiple jobs running on multiple threads, leading to a segmentation fault due to concurrent read/write in this function.