$ git clone -n https://src.fedoraproject.org/rpms/rust-arbitrary.git /var/lib/mock/f41-build-side-1-2934410-35233/root/chroot_tmpdir/scmroot/rust-arbitrary
Cloning into '/var/lib/mock/f41-build-side-1-2934410-35233/root/chroot_tmpdir/scmroot/rust-arbitrary'...
$ git fetch origin c5f1edf5d766dfdc8c407e40700bfd3a32750fae:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-arbitrary
 * [new ref]         c5f1edf5d766dfdc8c407e40700bfd3a32750fae -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c5f1edf Update to version 1.3.2; Fixes RHBZ#2243342