Test both PHP 7.4 and PHP 8.0 in CI

Author: aboks

.github/workflows/ci.yml

@@ -11,10 +11,19 @@ jobs:
 
     runs-on: ubuntu-latest
 
+    strategy:
+      matrix:
+        php-version: [ '7.4', '8.0' ]
+
     steps:
     - name: Checkout code
       uses: actions/checkout@v2
 
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php-version }}
+
     - name: Validate composer.json and composer.lock
       run: composer validate