Fix CI dependencies step

Author: vincent-pochet

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
         run: |
-          python -m pip install --upgrade pip
+          pip install .
       - name: Display Python version
         run: python -c "import sys; print(sys.version)"
       - name: Run tests