CI: Install package in tests workflow to ensure importability

Author: pr4bh4sh

.github/workflows/tests.yml

@@ -25,6 +25,7 @@ jobs:
         python -m pip install --upgrade pip
         python -m pip install pytest pytest-xdist
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+        pip install -e .
     - name: Run tests (Parallel)
       run: |
         pytest -n auto