Use actions/setup-python@v4 with built-in caching.

`actions/setup-python@v4` supports caching built-in: https://github.com/actions/setup-python#caching-packages-dependencies. Discovered when reviewing cache mechanisms for cl/587110684.

PiperOrigin-RevId: 587828085

.github/workflows/ci-build.yml

@@ -47,19 +47,10 @@ jobs:
       if: ${{github.ref != 'refs/head/main'}}
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
-    - name: Get pip cache dir
-      id: pip-cache
-      run: |
-        python -m pip install --upgrade pip wheel
-        echo "::set-output name=dir::$(pip cache dir)"
-    - name: pip cache
-      uses: actions/cache@v2
-      with:
-        path: ${{ steps.pip-cache.outputs.dir }}
-        key: ${{ runner.os }}-pip-${{ hashFiles('**/setup.py') }}
+        cache: 'pip'
     - name: Install Xee
       run: |
         pip install -e .[tests]