Now, `_post_copy()` is only called when the module is installed for the
first time on a website, not when the module is updated.
See counterpart commit in community for more details.
opw-2824045
closesodoo/design-themes#562
Related: odoo/odoo#91012
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>