Use latest GitHub action version

Author: sandrokeil

.github/workflows/integration.yml

@@ -20,10 +20,10 @@ jobs:
     continue-on-error: ${{ matrix.experimental }}
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v2.3.1"
+        uses: actions/checkout@v2
 
       - name: "Install PHP"
-        uses: "shivammathur/setup-php@2.4.1"
+        uses: shivammathur/setup-php@v2
         with:
           php-version: "${{ matrix.php-version }}"
           coverage: xdebug