ci: install ApiProber before smoke tests

Author: Lukas Geiger

.github/workflows/tests.yml

@@ -30,6 +30,9 @@ jobs:
       - name: Install test dependencies
         run: python -m pip install --upgrade pip pytest
 
+      - name: Install ApiProber package
+        run: python -m pip install -e .
+
       - name: Run smoke tests
         run: python -m pytest -q