ci: Use `dnf builddep`, enable rpm-ostree by default

We use this pattern in the ostree CI, no reason to replicate
all of the build dependencies here.
And enable-rpm-ostree CI.
1 job for ci-rpmostree in 5 minutes and 54 seconds (queued for 2 seconds)
latest
Status Name Job ID Coverage
  Build
passed build-gnome-software #33627

00:05:54