Add PHP 8.1 to build matrix

Author: aboks

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
 
         strategy:
             matrix:
-                php-version: [ '7.3', '7.4', '8.0' ]
+                php-version: [ '7.3', '7.4', '8.0', '8.1' ]
 
         steps:
             - name: Checkout code