Use BinaryMutex instead of Mutex for StringName.

core/object/object.cpp

@@ -2226,6 +2226,16 @@ void Object::detach_from_objectdb() {
 	}
 }
 
+void Object::assign_class_name_static(const Span<char> &p_name, StringName &r_target) {
+	static BinaryMutex _mutex;
+	MutexLock lock(_mutex);
+	if (r_target) {
+		// Already assigned while we were waiting for the mutex.
+		return;
+	}
+	r_target = StringName(p_name.ptr(), true);
+}
+
 Object::~Object() {
 	if (script_instance) {
 		memdelete(script_instance);