ci: Replace only/except with rules

ci: Replace only/except with rules

only/except keywords where deperecated in favor of rules.

Since we started using GNOME/gnome-shell!1492 it introduced
a second pipeline being run for each commit.

Detached pipelines are the only way to access CI_MERGE_REQUEST_*
variables, and if we disable normal pipelines you will need to
create wip/spam MRs in order to run the tests.

This reworked rules makes it so, the normal pipeline needs manual
interaction to be started, and the detached/MR pipleines is always
run.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1503>