[Backport 2.x] Exclude 'benchmarks' from codecov report

[opensearch-trigger-bot]

Backport 78537a2 from #8805.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/20683/
• CommitID: fc323a0
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[kotwanikunal]

#8395

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.indices.replication.SegmentReplicationIT.testDropPrimaryDuringReplication

• URL: https://build.ci.opensearch.org/job/gradle-check/20689/
• CommitID: fc323a0
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8822 (fc323a0) into 2.x (18fc75f) will increase coverage by 0.22%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #8822      +/-   ##
============================================
+ Coverage     70.62%   70.84%   +0.22%     
- Complexity    57350    57379      +29     
============================================
  Files          4758     4744      -14     
  Lines        271525   271061     -464     
  Branches      40029    39977      -52     
============================================
+ Hits         191760   192040     +280     
+ Misses        63297    62566     -731     
+ Partials      16468    16455      -13     

see 472 files with indirect coverage changes