Set PYTHONPATH for install step in CI workflow

Added PYTHONPATH environment variable pointing to versioning/helper during the "Install the project" step in the CI workflow. This ensures Python can locate necessary modules during installation.

Author: sellakumaran

.github/workflows/ci.yml

@@ -105,6 +105,8 @@ jobs:
 
     - name: Install the project
       run: uv lock && uv sync --locked --all-extras --dev
+      env:
+        PYTHONPATH: ${{ github.workspace }}/versioning/helper
 
     - name: Verify centralized version constraints
       run: uv run --frozen tox -e verify-constraints