Osquerybeat: Follow up with changelog and unit test tweak for "Add action responses data stream PR"

[aleksmaus]

Proposed commit message

Osquerybeat: Follow up with changelog and unit test tweak for "Add action responses data stream PR"

This addresses a few PR comments related to a missing changelog entry and the unit test code.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Relates Osquerybeat: Add action responses data stream #39143

@pkoutsovasilis @mjwolf this addresses the comments that I missed from the previous PR review. Please review.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @aleksmaus? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

Pinging @elastic/sec-deployment-and-devices (Team:Security-Deployment and Devices)

[aleksmaus]

/test

[pkoutsovasilis]

LGTM