$ git clone -n https://src.fedoraproject.org/rpms/rust-base64ct.git /var/lib/mock/f42-build-side-1-3586737-46924/root/chroot_tmpdir/scmroot/rust-base64ct
Cloning into '/var/lib/mock/f42-build-side-1-3586737-46924/root/chroot_tmpdir/scmroot/rust-base64ct'...
$ git fetch origin 846636ac63fab383d8f98448c0807dbf2d046020:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-base64ct
 * [new ref]         846636ac63fab383d8f98448c0807dbf2d046020 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 846636a Update to version 1.8.0; Fixes RHBZ#2370268