Update CI for Moodle 5.1 (MDL-85362)

Author: james-cnz

.github/workflows/moodle-ci.yml

@@ -11,7 +11,7 @@ jobs:
 
     services:
       postgres:
-        image: postgres:14 # Moodle 5.0
+        image: postgres:15 # Moodle 5.1
         env:
           POSTGRES_USER: 'postgres'
           POSTGRES_HOST_AUTH_METHOD: 'trust'