Update workflow to actions/cache v4

Author: joedolson

.github/workflows/main.yml

@@ -30,7 +30,7 @@ jobs:
     timeout-minutes: 20
     steps:
       - uses: styfle/cancel-workflow-action@0.8.0
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: '7.4'