[FIX] tests: Make `at_install` and `post_install` backwards compatible
[FIX] tests: Make `at_install` and `post_install` backwards compatible

Fixes #27471 by just using `tagged()` behind the scenes.

calls to `tagged` were done in the wrong order

closes odoo/odoo#27531
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo