Update actions/checkout action to v4

| datasource  | package          | from | to |
| ----------- | ---------------- | ---- | -- |
| github-tags | actions/checkout | v3   | v4 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/continuous-integration.yml

@@ -16,7 +16,7 @@ jobs:
     name: PHPUnit Coverage
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: shivammathur/setup-php@2.25.5
         with:
           php-version: 8.1
@@ -40,7 +40,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: "Install PHP"
         uses: shivammathur/setup-php@2.25.5