Change into project directory before printing pipeline in culprit_finder.py (#2438)

This PR fixes a bug in `culprit_finder.py` where it fails to find the
local CI config file (e.g., `.bazelci/presubmit.yml`) because it doesn't
change into the cloned project directory.

Changes:
- Store the directory returned by `clone_git_repository`.
- Change into that directory before calling
`print_culprit_finder_pipeline`.