fix unittest runner

Author: pfefferle

.github/workflows/phpunit.yml

@@ -18,6 +18,8 @@ jobs:
         php-versions: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
         include:
           - wp-version: latest
+          - wp-version: '6.5'
+            php-versions: ['7.0', '7.1']
     steps:
       - name: Checkout
         uses: actions/checkout@v2