caching python dependencies

.github/workflows/test_Ch02.yml

@@ -21,6 +21,10 @@ jobs:
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - uses: actions/checkout@v3
+      - uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+          cache: 'pip'
 
       # Install
       - name: Install dependencies