Merge branch 'tb/commit-graph-tests'

Test updates. * tb/commit-graph-tests: t/lib-commit-graph.sh: avoid sub-shell in `graph_git_behavior()` t5328: avoid top-level directory changes t5318: avoid top-level directory changes t/lib-commit-graph.sh: avoid directory change in `graph_git_behavior()` t/lib-commit-graph.sh: allow `graph_read_expect()` in sub-directories