Merge branch 'ld/sparse-diff-blame'

Teach diff and blame to work well with sparse index. * ld/sparse-diff-blame: blame: enable and test the sparse index diff: enable and test the sparse index diff: replace --staged with --cached in t1092 tests repo-settings: prepare_repo_settings only in git repos test-read-cache: set up repo after git directory commit-graph: return if there is no git directory git: ensure correct git directory setup with -h