Merge branch 'tb/stdin-packs-excluded-but-open'

pack-objects's --stdin-packs=follow mode learns to handle excluded-but-open packs. * tb/stdin-packs-excluded-but-open: repack: mark non-MIDX packs above the split as excluded-open pack-objects: support excluded-open packs with --stdin-packs t7704: demonstrate failure with once-cruft objects above the geometric split pack-objects: refactor `read_packs_list_from_stdin()` to use `strmap` pack-objects: plug leak in `read_stdin_packs()`