$ git clone -n https://src.fedoraproject.org/rpms/ghc-reducers.git /var/lib/mock/f39-build-1713262-41228/root/chroot_tmpdir/scmroot/ghc-reducers
Cloning into '/var/lib/mock/f39-build-1713262-41228/root/chroot_tmpdir/scmroot/ghc-reducers'...
$ git fetch origin 85b61591acf06b43062c38d1c295719fe84123b5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ghc-reducers
 * [new ref]         85b61591acf06b43062c38d1c295719fe84123b5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 85b6159 revised .cabal file