Add PHP 8.3, 8.4, and 8.5 to test matrix

Expanded the GitHub Actions PHPUnit workflow to include PHP versions 8.3, 8.4, and 8.5 in the test matrix for broader compatibility testing.

Author: pfefferle

.github/workflows/phpunit.yml

@@ -12,7 +12,7 @@ jobs:
 
     strategy:
       matrix:
-        php-version: ['7.4', '8.0', '8.1', '8.2']
+        php-version: ['7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5']
         wp-version: ['6.5', 'latest']
 
     services: