$ git clone -n https://src.fedoraproject.org/rpms/tcl-snack.git /var/lib/mock/f40-build-789957-136170/root/chroot_tmpdir/scmroot/tcl-snack
Cloning into '/var/lib/mock/f40-build-789957-136170/root/chroot_tmpdir/scmroot/tcl-snack'...
$ git fetch origin a861fb911745d852c7268a33e4575c101a0fea81:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/tcl-snack
 * [new ref]         a861fb911745d852c7268a33e4575c101a0fea81 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a861fb9 fix FTBFS