Upgrade to actions/cache v4

v2 is gone now

Author: mdio

.github/workflows/tests.yml

@@ -25,7 +25,7 @@ jobs:
 
       - name: Cache Composer packages
         id: composer-cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: vendor
           key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}