Update gnomeos jobs for 2.58 / GNOME 46
From #1043 (comment 2003322):
We should also remove the Nightly CI tests when branching, and bump the stable images to 46. Images should get pushed once we branch 46.Beta.
@alatiera can we have a rules
so that the jobs for rust-nightly don't get run on stable branches? I think we can just test the branch name for main
?