[2.x] Add [2.x] to dependabot commit message

[cwperks]

Description

Prefixes the dependabot commit message with [2.x] for PRs against the 2.x branch.

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Maintenance

Check List

• New functionality includes testing
• New functionality has been documented
• 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.

[codecov]

Codecov Report

Merging #3219 (94d0947) into 2.x (478b27d) will decrease coverage by 2.38%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #3219      +/-   ##
============================================
- Coverage     62.21%   59.83%   -2.38%     
+ Complexity     3313     3199     -114     
============================================
  Files           265      265              
  Lines         19508    19508              
  Branches       3329     3329              
============================================
- Hits          12137    11673     -464     
- Misses         5744     6221     +477     
+ Partials       1627     1614      -13     

see 23 files with indirect coverage changes

[cwperks]

Bwc test failure is due to compilation error on 2.x.

The compilation error is due to a bad import in CredentialsValidator which was removed on main in this PR that was not backported to 2.x yet.

Build started failing on 2.x an hour ago after the merge of this PR: opensearch-project/OpenSearch#9367