Update push.yml

Author: dereuromark

.github/workflows/push.yml

@@ -49,7 +49,7 @@ jobs:
       matrix:
         operating-system:
           - ubuntu-latest
-        php-versions: ['7.2', '7.3', '7.4', '8.0']
+        php-versions: ['7.2', '7.3', '7.4', '8.0', '8.1']
     name: Unit tests for PHP version ${{ matrix.php-versions }} on ${{ matrix.operating-system }}
     needs:
       - phpunit-with-coverage