$ git clone -n https://src.fedoraproject.org/rpms/rust-derp.git /var/lib/mock/f45-build-41247-780/root/chroot_tmpdir/scmroot/rust-derp
Cloning into '/var/lib/mock/f45-build-41247-780/root/chroot_tmpdir/scmroot/rust-derp'...
$ git fetch origin 742b7daf42f656e09538ce1504e195176d227fa6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-derp
 * [new ref]         742b7daf42f656e09538ce1504e195176d227fa6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 742b7da Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild