$ git clone -n https://src.fedoraproject.org/rpms/gtk-vnc.git /var/lib/mock/f42-build-3357721-45030/root/chroot_tmpdir/scmroot/gtk-vnc
Cloning into '/var/lib/mock/f42-build-3357721-45030/root/chroot_tmpdir/scmroot/gtk-vnc'...
$ git fetch origin 51bec8e52b56caf8af910bfcc3a16065b10d1b0a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gtk-vnc
 * [new ref]         51bec8e52b56caf8af910bfcc3a16065b10d1b0a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 51bec8e Fix --gtk-vnc-debug flag with new glib2