[PYG-348] 🤕 fix: ensure output dir is a path

[doctrino]

Description

Please describe the change you have made.

Checklist:

• Tests added/updated.
• Documentation updated.
• Changelog updated in CHANGELOG.md.
• Version bumped. If triggering a new release is desired (?), bump the version number by running python dev.py bump --patch (replace --patch with --minor or --major per semantic versioning).
• Regenerate example SDKs export PYTHONPATH=. && python dev.py generate. Need to be run both
  for pydantic v1 and v2 environments.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
4734	3353	71%	60%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
cognite/pygen/_generator.py	76%	🟢
TOTAL	76%	🟢

updated for commit: 701b4ac by action🐍