chore(deps): update actions/cache action to v4

Author: renovate[bot]

.github/workflows/python-ci.yml

@@ -24,7 +24,7 @@ jobs:
         run: pip install pipenv
 
       - name: Cache virtual environment
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.local/share/virtualenvs
           key: ${{ runner.os }}-python-${{ steps.setup-python.outputs.python-version }}-pipenv-${{ hashFiles('Pipfile.lock') }}