$ git clone -n https://src.fedoraproject.org/rpms/cppcodec.git /var/lib/mock/f40-build-791211-137268/root/chroot_tmpdir/scmroot/cppcodec
Cloning into '/var/lib/mock/f40-build-791211-137268/root/chroot_tmpdir/scmroot/cppcodec'...
$ git fetch origin 5b1f69c9b6ec46d19e0b9a3e4c7841645b394fbb:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/cppcodec
 * [new ref]         5b1f69c9b6ec46d19e0b9a3e4c7841645b394fbb -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5b1f69c FTBFS fix