[Backport 1.3] Updated 1.3.9 release note to include latest version of Netty

[opensearch-trigger-bot]

Backport 973ba4f from #6698.

[codecov-commenter]

Codecov Report

Merging #6720 (fd81583) into 1.3 (fd81583) will not change coverage.
The diff coverage is n/a.

❗ Current head fd81583 differs from pull request most recent head 73f539f. Consider uploading reports for the commit 73f539f to get more accurate results

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@@            Coverage Diff            @@
##                1.3    #6720   +/-   ##
=========================================
  Coverage     77.89%   77.89%           
  Complexity    63464    63464           
=========================================
  Files          4454     4454           
  Lines        274963   274963           
  Branches      41167    41167           
=========================================
  Hits         214178   214178           
  Misses        43883    43883           
  Partials      16902    16902           

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/12539/
• CommitID: 73f539f

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: SUCCESS ✅
• URL: https://build.ci.opensearch.org/job/gradle-check/12542/
• CommitID: 73f539f