Update actions/cache@v4 and actions/checkout@v4

> The following actions use a deprecated Node.js version and will be forced to run on node20: actions/checkout@v3, actions/cache@v3. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

.github/workflows/ci.yml

@@ -15,14 +15,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Validate composer.json and composer.lock
         run: composer validate --strict
 
       - name: Cache Composer packages
         id: composer-cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: vendor
           key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}