fix: Update actions/cache version (#118)

Author: Reikyo

.github/workflows/tests.yaml

@@ -31,7 +31,7 @@ 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') }}