Fixes #3412. Prevent users from being able to modify their own groups.

modules/backend/models/user/fields.yaml

@@ -53,6 +53,7 @@ tabs:
             type: radio
 
         groups:
+            context: [create, update]
             label: backend::lang.user.groups
             commentAbove: backend::lang.user.groups_comment
             type: checkboxlist
@@ -66,4 +67,3 @@ secondaryTabs:
             mode: image
             imageHeight: 250
             imageWidth: 250
-