Update ci.yml (#84)

* Update to actions/checkout@4
* Test on PHP 8.3 and 8.4

Author: reedy

.github/workflows/ci.yml

@@ -14,10 +14,10 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2']
+        php-version: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up PHP ${{ matrix.php-version }}
         uses: shivammathur/setup-php@v2
         with: