ci: Add pip cache

Author: timo-reymann

.github/workflows/main.yml

@@ -15,6 +15,7 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: 3.12
+          cache: 'pip'
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
       - run: |