Merge branch 'master' of github.com:git/git

* 'master' of github.com:git/git: (63 commits)
  Git 2.31-rc1
  Hopefully the last batch before -rc1
  Revert "commit-graph: when incompatible with graphs, indicate why"
  read-cache: make the index write buffer size 128K
  dir: fix malloc of root untracked_cache_dir
  commit-graph.c: display correct number of chunks when writing
  doc/reftable: document how to handle windows
  fetch-pack: print and use dangling .gitmodules
  fetch-pack: with packfile URIs, use index-pack arg
  http-fetch: allow custom index-pack args
  http: allow custom index-pack args
  chunk-format: add technical docs
  chunk-format: restore duplicate chunk checks
  midx: use 64-bit multiplication for chunk sizes
  midx: use chunk-format read API
  commit-graph: use chunk-format read API
  chunk-format: create read chunk API
  midx: use chunk-format API in write_midx_internal()
  midx: drop chunk progress during write
  midx: return success/failure in chunk write methods
  ...