update remaining GitHub actions

Author: xabbuh

.github/workflows/ci.yaml

@@ -94,7 +94,7 @@ jobs:
 
     steps:
       - name: 'Check out'
-        uses: 'actions/checkout@v2'
+        uses: 'actions/checkout@v4'
 
       - name: 'Set up PHP'
         uses: 'shivammathur/setup-php@v2'
@@ -107,7 +107,7 @@ jobs:
         run: 'echo "::set-output name=cache-dir::$(composer config cache-files-dir)"'
 
       - name: 'Cache dependencies'
-        uses: 'actions/cache@v2'
+        uses: 'actions/cache@v4'
         with:
           path: '${{ steps.composer-cache.outputs.cache-dir }}'
           key: "php-${{ matrix.php-version }}-composer-locked-${{ hashFiles('composer.lock') }}"