$ git clone -n https://src.fedoraproject.org/rpms/rust-git2.git /var/lib/mock/f40-build-2092273-50268/root/chroot_tmpdir/scmroot/rust-git2
Cloning into '/var/lib/mock/f40-build-2092273-50268/root/chroot_tmpdir/scmroot/rust-git2'...
$ git fetch origin 0e4e25fdaf4e86cb22956c59c50030066acc20d0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2
 * [new ref]         0e4e25fdaf4e86cb22956c59c50030066acc20d0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0e4e25f Update to version 0.18.1; Fixes RHBZ#2239943