Before this commit, the title of the SelectCreateDialog opened
when clicking on "Add a line" in a Many2ManyField was always
"Select Records" (the default value), whereas in this case, we
want to see "Add: something", where `something` is the `string`
attribute of the field (which can be overriden by an attrs on the
field node in the arch). This commit restores the desired behavior.
closesodoo/odoo#100046
Signed-off-by: Géry Debongnie <ged@odoo.com>