Merge branch 'ps/repack-avoid-noop-midx-rewrite' into tb/midx-write-corrupt-checksum-fix

* 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