Add PHP 8.4 and 8.5 to unit test matrix

- Add PHP 8.4 and 8.5 as experimental test builds
- Allows monitoring compatibility with latest PHP versions
- Tests won't block CI if they fail (experimental: true)

Author: ajaydsouza

.github/workflows/unit-tests.yml

@@ -31,6 +31,13 @@ jobs:
           # Complement the builds run via the matrix with high/low WP builds for PHP 7.4 and 8.0.
           # PHP 8.0 is sort of supported since WP 5.6.
           # PHP 7.4 is supported since WP 5.3.
+          - php: '8.5'
+            wp: 'latest'
+            experimental: true
+          - php: '8.4'
+            wp: 'latest'
+            experimental: true
+
           - php: '8.3'
             wp: 'latest'
             experimental: true