Check property referecne name when the property is created

com.unity.shadergraph/Editor/Drawing/Blackboard/BlackboardProvider.cs

                 return;
 
             if (create)
+            {
+                property.overrideReferenceName = m_Graph.SanitizePropertyReferenceName(property.overrideReferenceName);
+            }
 
             var field = new BlackboardField(m_ExposedIcon, property.displayName, property.propertyType.ToString()) { userData = property };
             var row = new BlackboardRow(field, new BlackboardFieldPropertyView(m_Graph, property));