Merge branch 'ps/repack-avoid-noop-midx-rewrite'

Even when there is no changes in the packfile and no need to recompute bitmaps, "git repack" recomputed and updated the MIDX file, which has been corrected. * ps/repack-avoid-noop-midx-rewrite: midx-write: skip rewriting MIDX with `--stdin-packs` unless needed midx-write: extract function to test whether MIDX needs updating midx: fix `BUG()` when getting preferred pack without a reverse index