$ git clone -n https://src.fedoraproject.org/rpms/gnome-music.git /var/lib/mock/f42-build-side-1-3498257-45962/root/chroot_tmpdir/scmroot/gnome-music
Cloning into '/var/lib/mock/f42-build-side-1-3498257-45962/root/chroot_tmpdir/scmroot/gnome-music'...
$ git fetch origin 5074a4cb3319b94909d41934494ea67dbca933d3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gnome-music
 * [new ref]         5074a4cb3319b94909d41934494ea67dbca933d3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5074a4c Rebuild against a side tag