Update actions/cache.

Author: luciansmith

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
           python-version: '3.9'
 
       - name: Setup pip cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: /opt/hostedtoolcache/Python
           key: ${{ runner.os }}-pip-${{ hashFiles('site_creator/requirements.txt') }}