opw-1920590
Before this commit, the function prepare_backend_url forced in the url
the view_type 'form'. This occurs because a misunderstand between the
fields ir.actions.act_window.view_type (That indicate if an hierarchy
in the view list exists, with as possible values : form and tree, which
can be mistaken as views types) and ir.actions.act_window.view_mode
(which is a list of allowed views).
Now, if not ask otherwise, the function give the url of the first
(the default) allowed view; or one of the allowed view if asked for it.
closesodoo/odoo#29882