[backup] Don't display false-positive warn

Summary:
Described in [[ https://linear.app/comm/issue/ENG-10179/investigate-why-backup-wasnt-removed-during-keyserver-owner-logout#comment-73457631 | ENG-10179 ]].
The warning is false-positive when limit is set because `last_evaluated_key` is present in that case.

Test Plan: Tested on staging, real world scenario we were encountering seems not to be reproducible on localstack.

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14372

services/backup/src/database/mod.rs

@@ -370,7 +370,7 @@ impl DatabaseClient {
         Error::AwsSdk(e.into())
       })?;
 
-    if response.last_evaluated_key().is_some() {
+    if response.last_evaluated_key().is_some() && limit.is_none() {
       // In the intial version of the backup service this function will be run
       // for every new backup (each user only has one backup), so this shouldn't
       // happen