Fix: Order of node mixins in custom nodes python template

See T101259. This order makes the poll not work, even when called from
Python. The bundled template shouldn't be a source of errors for node
addons.

release/scripts/templates_py/custom_nodes.py

@@ -61,7 +61,7 @@ class MyCustomTreeNode:
 
 
 # Derived from the Node base type.
-class MyCustomNode(Node, MyCustomTreeNode):
+class MyCustomNode(MyCustomTreeNode, Node):
     # === Basics ===
     # Description string
     '''A custom node'''