Revise test-postgres matrix

Author: Andy Babic

.github/workflows/test.yml

@@ -133,7 +133,7 @@ jobs:
       matrix:
         python-version: ["3.12"]
         django: ["5.0", "5.1"]
-        wagtail: ["6.0", "6.2", "6.3"]
+        wagtail: ["6.2", "6.3"]
         db: ["postgres"]
 
     services: