Run unit tests against installed BeeRef package instead of source directory

This way, we can test whether setup.py picks up all source files.

.github/workflows/pytest.yml

@@ -23,6 +23,11 @@ jobs:
           sudo apt install xvfb
           python -m pip install --upgrade pip
           pip install .
+          # We want to test against installed package instead of source files
+          pip install . --target beeref_inst
+          rm -r beeref
+          mv beeref_inst/beeref beeref
+          rm -r beeref_inst
           pip install -r requirements/test.txt
           pip install pyQt6==${{ matrix.pyqt-version }} pyQt6-Qt6==${{ matrix.pyqt-version }} --upgrade
       - name: Run Unittests with pytest