$ git clone -n https://src.fedoraproject.org/rpms/rust-test-tag.git /var/lib/mock/f41-build-side-1-2983936-35892/root/chroot_tmpdir/scmroot/rust-test-tag
Cloning into '/var/lib/mock/f41-build-side-1-2983936-35892/root/chroot_tmpdir/scmroot/rust-test-tag'...
$ git fetch origin 70a613cbbf83b8a49ce830e1c676494ab3d4985c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-test-tag
 * [new ref]         70a613cbbf83b8a49ce830e1c676494ab3d4985c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 70a613c Initial package (rhbz#2299423)