$ git clone -n https://src.fedoraproject.org/rpms/ghc-aeson.git /var/lib/mock/f39-build-1938900-43148/root/chroot_tmpdir/scmroot/ghc-aeson
Cloning into '/var/lib/mock/f39-build-1938900-43148/root/chroot_tmpdir/scmroot/ghc-aeson'...
$ git fetch origin 54bff12153f6e8f1a04f267e443b0f3c1a014785:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ghc-aeson
 * [new ref]         54bff12153f6e8f1a04f267e443b0f3c1a014785 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 54bff12 update to 2.1.2.1; add generically