upgrade-python-tree-view (U1809)

Python code refers to the tree view type, renamed list in Odoo 18.0.

Applies to Odoo 18.0 and later.

What it does

Reports tree in action dictionaries built in Python: a view_mode value such as "tree,form", (view_id, "tree") in views, and tree_view_ref keys in contexts.

Why is this bad?

Since Odoo 18.0 the view type is list. An action with tree fails when it is opened, and tree_view_ref is silently ignored.

Fix safety

Safe: the strings are changed in place.