Merge branch 'ab/ignore-replace-while-working-on-commit-graph'

Merge branch 'ab/ignore-replace-while-working-on-commit-graph'

Teach "git commit-graph" command not to allow using replace objects
at all, as we do not use the commit-graph at runtime when we see
object replacement.

* ab/ignore-replace-while-working-on-commit-graph:
  commit-graph: don't consider "replace" objects with "verify"
  commit-graph tests: fix another graph_git_two_modes() helper
  commit-graph tests: fix error-hiding graph_git_two_modes() helper