Update php.yml

.github/workflows/php.yml

@@ -8,9 +8,17 @@ on:
 
 jobs:
   build:
+      strategy:
+        matrix:
+          php: ['5.6.40']
+          os: ['ubuntu-16.04']
+          include:
+            - php: '5.6.40'
+              os: 'ubuntu-16.04'
     
-    runs-on: ubuntu-16.04
+      runs-on: ${{ matrix.os }}
-
+      env:
+          PHP_VERSION: ${{ matrix.php }}
       steps:
       - uses: actions/checkout@v2