Update sys.path.appends to use Path object

Background

To remain consistent with how we gather parent directories in other contexts, we should update sys.path.append to use a Path object to get parent directories where needed (e.g. for test_* files to import the module they're testing).

Example:

import sys
import os
sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))

should be

import sys
from pathlib import Path
sys.path.append(Path(__file__).absolute().parents[1])))

Acceptance Criteria

• All sys.path.appends use a Path object instead of os
  • test_pipeline_csv_gen.py
  • test_downloader.py
  • test_base_image_validation.py
  • test_dockerfile_validation.py
  • test_folder_structure.py
  • test_hardening_manifest_validation.py
  • test_pipeline_auth_status.py
  • test_upload_artifacts.py
  • test_image_verify.py
  • test_scan_logic_jobs.py
  • test_trufflehog.py

Definition of Done

• Write or update any unit or integration tests
• Project pipeline runs successfully
• Solution is captured as code and/or documentation and merge requests have been submitted
• Code review completed and merge request approved/merged
• All Acceptance Criteria have been completed