$ git clone -n https://src.fedoraproject.org/rpms/csdiff.git /var/lib/mock/f41-build-side-1-2633641-25947/root/chroot_tmpdir/scmroot/csdiff
Cloning into '/var/lib/mock/f41-build-side-1-2633641-25947/root/chroot_tmpdir/scmroot/csdiff'...
$ git fetch origin 505bf631d7d050a5c4b02fd9fb288f600cc6d58e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/csdiff
 * [new ref]         505bf631d7d050a5c4b02fd9fb288f600cc6d58e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 505bf63 make it possible to create SRPM from a git tree