Fix the build
    
    We can't conditionally include the flatpak patch as the flatpak macro
    isn't defined when building the srpm in koji, which means that the patch
    doesn't get included in the srpm and the flatpak build fails due to not
    finding the patch file.
    
    As a fix, change it so that the flatpak patch is always included in the
    srpm, but only conditionally applied when building for flatpak.
    
    While at this, also guard gschema.xml %files entry with 0%{?flatpak} to
    fix the non-flatpak build.