Fix race condition in testThrottlingForSingleNode.

[dblock]

Signed-off-by: dblock dblock@dblock.org

Description

Missed this one. It failed in #5153

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/6635/
• CommitID: b1db611
  Please examine the workflow log, locate, and copy-paste the failure below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[dblock]

org.opensearch.action.bulk.BulkIntegrationIT.testDeleteIndexWhileIndexing

#5162

[reta]

Gradle Check (Jenkins) Run Completed with:

* **RESULT:** UNSTABLE ❌

* **URL:** https://build.ci.opensearch.org/job/gradle-check/6635/

* **CommitID:** [b1db611](https://github.com/opensearch-project/OpenSearch/commit/b1db61100b75a60723128faf52596c77d3f66a24)
  Please examine the workflow log, locate, and copy-paste the failure below, then iterate to green.
  Is the failure [a flaky test](https://github.com/opensearch-project/OpenSearch/blob/main/DEVELOPER_GUIDE.md#flaky-tests) unrelated to your change?

Hm ... this is a new one, haven't been flaky (AFAIK) so far:

org.opensearch.action.bulk.BulkIntegrationIT.testDeleteIndexWhileIndexing

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/6648/
• CommitID: b1db611