$ git clone -n https://src.fedoraproject.org/rpms/gcab.git /var/lib/mock/f39-build-1519172-35815/root/chroot_tmpdir/scmroot/gcab
Cloning into '/var/lib/mock/f39-build-1519172-35815/root/chroot_tmpdir/scmroot/gcab'...
$ git fetch origin 5e6f64d8711453ec2d78d9ed68016f3a55fe87a6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gcab
 * [new ref]         5e6f64d8711453ec2d78d9ed68016f3a55fe87a6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5e6f64d Add MinGW packages