GenerateUnsetUserKeys: only select necessary user fields

priv/repo/migrations/20220905011454_generate_unset_user_keys.exs

@@ -14,7 +14,7 @@ def change do
       from(u in User,
         where: u.local == true,
         where: is_nil(u.keys),
-        select: u
+        select: struct(u, [:id, :keys])
       )
 
     Repo.stream(query)