Merge branch 'ds/midx-write-repack-fix'

Repacking a repository with multi-pack index started making stupid
pack selections in Git 2.45, which has been corrected.

* ds/midx-write-repack-fix:
  midx-write: revert use of --stdin-packs
  t5319: add failing test case for repack/expire

diff --cc midx-write.c
Simple merge

diff --cc t/t5319-multi-pack-index.sh
Simple merge