ci: Add PHP 8.0 and greater to build matrix

Author: DannyvdSluijs

.github/workflows/continuous-integration.yml

@@ -26,7 +26,10 @@ jobs:
           - "7.2"
           - "7.3"
           - "7.4"
-#          - "8.0"
+          - "8.0"
+          - "8.1"
+          - "8.2"
+          - "8.3"
         dependencies: [highest]
         experimental: [false]
         include: