Fix admin loop (#2103)

* mailbox page requires sudo

* fix the loop when non-admin user visits an admin URL

https://github.com/simple-login/app/issues/2101

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Co-authored-by: Son NK <son@simplelogin.io>

app/admin_model.py

@@ -46,7 +46,8 @@ class SLModelView(sqla.ModelView):
 
     def inaccessible_callback(self, name, **kwargs):
         # redirect to login page if user doesn't have access
-        return redirect(url_for("auth.login", next=request.url))
+        flash("You don't have access to the admin page", "error")
+        return redirect(url_for("dashboard.index", next=request.url))
 
     def on_model_change(self, form, model, is_created):
         changes = {}