Merge branch 'ab/commit-graph-usage'

Fixes on usage message from "git commit-graph". * ab/commit-graph-usage: commit-graph: show "unexpected subcommand" error commit-graph: show usage on "commit-graph [write|verify] garbage" commit-graph: early exit to "usage" on !argc multi-pack-index: refactor "goto usage" pattern commit-graph: use parse_options_concat() commit-graph: remove redundant handling of -h commit-graph: define common usage with a macro