Bumps 3.x BWC Test version to 2.12

[joshpalis]

Description

#526 must be merged first

Bumps up main branch's BWC test version to the latest 2.x

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[joshpalis]

Failing due to no 2.12 OS snapshot :

* What went wrong:
Execution failed for task ':opensearch-job-scheduler-sample-extension:jobSchedulerBwcCluster#oldVersionClusterTask1'.
> Could not resolve all files for configuration ':opensearch-job-scheduler-sample-extension:opensearch_distro_extracted_testclusters-opensearch-job-scheduler-sample-extension-jobSchedulerBwcCluster1-0-2.12.0-SNAPSHOT-'.
   > Could not resolve opensearch-distribution-snapshot:opensearch:2.12.0-SNAPSHOT.
     Required by:
         project :opensearch-job-scheduler-sample-extension
      > Could not resolve opensearch-distribution-snapshot:opensearch:2.12.0-SNAPSHOT.
         > Could not get resource 'https://artifacts.opensearch.org/snapshots/core/opensearch/2.12.0-SNAPSHOT/opensearch-min-2.12.0-SNAPSHOT-linux-x64-latest.tar.gz'.
            > Could not HEAD 'https://artifacts.opensearch.org/snapshots/core/opensearch/2.12.0-SNAPSHOT/opensearch-min-2.12.0-SNAPSHOT-linux-x64-latest.tar.gz'. Received status code 403 from server: Forbidden

@prudhvigodithi For your reference, it'll be necessary for a 2.12 OpenSearch distribution build to become available before we can re-run these checks.

[codecov]

Codecov Report

Merging #528 (75058fc) into main (7bd563f) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #528   +/-   ##
=========================================
  Coverage     29.17%   29.17%           
  Complexity       98       98           
=========================================
  Files            22       22           
  Lines          1186     1186           
  Branches        109      109           
=========================================
  Hits            346      346           
  Misses          819      819           
  Partials         21       21