packit: switch the remaining jobs to F35
    
    gcc-12 seems to be very unstable right now, so to keep our CI builds
    useful let's move them to stable F35 for a while.
    
    Follow-up to 478c632e00ffbf50012b1946a8a025494c012353.
    See:
      * https://github.com/systemd/systemd/issues/22215
      * https://bugzilla.redhat.com/show_bug.cgi?id=2043915