[8.11] [Synthetics] Supress API key errors when we have no monitors (#…

…171085) (#171109)

# Backport

This will backport the following commits from `main` to `8.11`:
- [[Synthetics] Supress API key errors when we have no monitors
(#171085)](#171085)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT
[{"author":{"name":"Shahzad","email":"shahzad31comp@gmail.com"},"sourceCommit":{"committedDate":"2023-11-13T15:49:18Z","message":"[Synthetics]
Supress API key errors when we have no monitors
(#171085)","sha":"b71a52c9f8ce739990d0cd360fc4d89d92a80b83","branchLabelMapping":{"^v8.12.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:uptime","release_note:skip","v8.12.0","v8.11.1"],"number":171085,"url":"https://github.com/elastic/kibana/pull/171085","mergeCommit":{"message":"[Synthetics]
Supress API key errors when we have no monitors
(#171085)","sha":"b71a52c9f8ce739990d0cd360fc4d89d92a80b83"}},"sourceBranch":"main","suggestedTargetBranches":["8.11"],"targetPullRequestStates":[{"branch":"main","label":"v8.12.0","labelRegex":"^v8.12.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/171085","number":171085,"mergeCommit":{"message":"[Synthetics]
Supress API key errors when we have no monitors
(#171085)","sha":"b71a52c9f8ce739990d0cd360fc4d89d92a80b83"}},{"branch":"8.11","label":"v8.11.1","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Shahzad <shahzad31comp@gmail.com>

x-pack/plugins/synthetics/server/synthetics_service/synthetics_service.ts

@@ -423,6 +423,9 @@ export class SyntheticsService {
     };
 
     for await (const result of finder.find()) {
+      if (result.saved_objects.length === 0) {
+        return;
+      }
       try {
         if (!output) {
           output = await this.getOutput();