Add newer PHP versions to automated testing workflow

Author: battye

.github/workflows/phpunit.yaml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: ['5.6', '7.0', '7.1']
+        php: ['7.0', '7.1', '7.2', '7.3', '7.4']
 
     name: PHP ${{ matrix.php }} tests
     steps: