Update actions/checkout action to v3

Author: renovate[bot]

.github/workflows/php.yml

@@ -17,7 +17,7 @@ jobs:
     name: PHP ${{ matrix.php-versions }} Test on ${{ matrix.operating-system }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Install PHP
         uses: shivammathur/setup-php@v2
         with: