Add tests for Wagtail 5.1 on main.yml

Author: katdom13

.github/workflows/main.yml

@@ -16,6 +16,7 @@ jobs:
           - "4.1"
           - "4.2"
           - "5.0"
+          - "5.1"
         exclude:
           - python-version: "3.11"
             wagtail-version: "4.1"