$ git clone -n https://src.fedoraproject.org/rpms/ghc-regex-base.git /var/lib/mock/f41-build-837783-159384/root/chroot_tmpdir/scmroot/ghc-regex-base
Cloning into '/var/lib/mock/f41-build-837783-159384/root/chroot_tmpdir/scmroot/ghc-regex-base'...
$ git fetch origin c3bd071575769d2155ad82ea133bb28a913df6b3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ghc-regex-base
 * [new ref]         c3bd071575769d2155ad82ea133bb28a913df6b3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c3bd071 refresh .cabal revision