Run tests on multiple PHP version

.github/workflows/php.yml

@@ -8,15 +8,19 @@ on:
   workflow_dispatch:
 
 jobs:
-  build:
-
-    runs-on: ubuntu-latest
+  test:
+    runs-on: ${{ matrix.operating-system }}
+    strategy:
+      matrix:
+        operating-system: [ ubuntu-latest ]
+        php: [ '7.1', '7.2', '7.3', '7.4']
+    name: Tests with PHP ${{ matrix.php }}
 
     steps:
     - uses: actions/checkout@v2
     - uses: nanasess/setup-php@master
       with:
-        php-version: '7.3'
+        php-version: ${{ matrix.php }}
 
     - name: Validate composer.json and composer.lock
       run: composer validate