Fix missing gitlabMergeRequestState for note webhook triggers.

[bluesky-adi]

What does this PR do?

Populates the gitlabMergeRequestState environment variable for Jenkins
builds triggered by GitLab Merge Request note (comment) webhooks.
This brings note-triggered builds in line with merge request event triggers.

Testing done

Manual reasoning-based validation.

• Compared NoteHookTriggerHandlerImpl with MergeRequestHookTriggerHandlerImpl
• Verified that merge request event handler already populates
  mergeRequestState in CauseData
• Applied the same field population for note-triggered builds
• Change is deterministic and uses data already present in the webhook payload

Automated tests were not added because:

• The project currently lacks isolated unit tests for webhook trigger handlers
• Setting up Jenkins + GitLab webhook simulation is non-trivial
• The change mirrors existing, production-tested logic

Related issue

Fixes #1823

[bluesky-adi]

Thanks for the review opportunity!

The failing CI appears unrelated to this change (no tests were modified or added).
This PR only adds mergeRequestState population using existing webhook payload data,
mirroring logic already present in MergeRequestHookTriggerHandlerImpl.

Happy to rebase or adjust if you’d like me to handle CI locally or add a safeguard.

[bluesky-adi]

Thanks for the update.

This change is logic-only and mirrors existing behavior from
MergeRequestHookTriggerHandlerImpl.

The CodeQL failure appears to be related to Java autobuild
limitations for Jenkins plugins rather than this change itself.

Happy to adjust or add guidance if a specific build step
is preferred by maintainers.

[krisstern]

I am actually seeing the following in the logs:

10:34:45  [ERROR] COMPILATION ERROR : 
10:34:45  [INFO] -------------------------------------------------------------
10:34:45  [ERROR] /home/jenkins/agent/workspace/Plugins_gitlab-plugin_PR-1848/src/main/java/com/dabsquared/gitlabjenkins/trigger/handler/note/NoteHookTriggerHandlerImpl.java:[89,71] incompatible types: com.dabsquared.gitlabjenkins.gitlab.hook.model.State cannot be converted to java.lang.String

[krisstern]

Did you actually test this change locally?