Github Actions: Add PHP 8.x

Author: Skouat

.github/workflows/tests.yml

@@ -17,6 +17,7 @@ jobs:
                     - php: '7.2'
                     - php: '7.3'
                     - php: '7.4'
+                    - php: '8.0'
 
         name: PHP ${{ matrix.php }}