try to add to path by another way

Author: patapenka-alexey

Diff for: .github/workflows/packing.yml

@@ -550,7 +550,7 @@ jobs:
       - name: Run tests
         run: |
           . .venv/bin/activate
-          export PYTHONPATH="$PYTHONPATH:."
+          export PYTHONPATH=$PYTHONPATH:.:./
           make test-pure-install
         if: matrix.target.dist == 'bookworm' || matrix.target.dist == 'noble'