fix python36 pip bug

Author: antoinedemathelin

.github/workflows/run-test.yml

@@ -27,7 +27,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
+        python -m pip install --upgrade --no-cache-dir pip
         pip install pytest pytest-cov codecov
         pip install -r requirements.txt
     - name: Install adapt