Remove duplicate Jenkins push trigger

[JP0P]

Summary

Remove the redundant githubPush() trigger from the multibranch Jenkins pipeline.

Why

GitHub Branch Source already handles repository push events for this multibranch pipeline. The declarative githubPush() block persists a second, generic GitHub push trigger on each child job, adding a repository-wide SCM-polling path alongside Branch Source.

This is a known source of build amplification. Builds #160 and #161 both built commit 7795512, and Jenkins attempted to queue another testMaestro build while #166 was running. Historical incidents with more than two duplicates may include additional webhook, indexing, replay, or queue causes; this PR removes one redundant trigger path but does not claim comprehensive deduplication.

disableConcurrentBuilds() remains enabled. It prevents simultaneous execution of the same child job, but duplicate requests may still remain queued.

Risk

Low. The final diff only removes three lines of Jenkins trigger configuration.

• GitHub Branch Source continues handling push builds.
• Branch-index triggering and the periodic multibranch scan remain available.
• Manual builds and disableConcurrentBuilds() remain unchanged.
• No application, build, artifact, test, deployment, or retry logic changes.

Both trigger mechanisms use Jenkins' /github-webhook/ endpoint, so githubPush() is not an independent delivery fallback. Any duplicate or missing webhook-delivery investigation is separate from removing this redundant scheduling path.

Validation

• After the updated Jenkinsfile ran, the child job no longer persisted GitHubPushTrigger.
• The duplicate seen during the transition occurred while the child still had its previously persisted trigger configuration.
• The current testMaestro job configuration contains no generic GitHub push trigger.
• A separate edge-tester rollout removed the same generic trigger while retaining immediate, targeted GitHub-triggered builds through Branch Source.
• CI and security checks pass.

Children that have not executed the updated Jenkinsfile may retain the old persisted trigger, and replaying a pre-change build can restore it.