FDN-4433 Remove add-labels Github workflow

[jackl]

This is now done in the scala-steward repository in the Jenkins pipeline.

Summary by CodeRabbit

• Chores
  • Removed an automated pull request labeling workflow
  • Updated automated merge workflow to enforce stricter execution conditions

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes involve GitHub Actions workflow modifications: removing a pull request labeling automation workflow and adding more restrictive conditions to the auto-merge workflow to only trigger on Jenkins-specific success events.

Changes

Cohort / File(s)	Summary
Labeling Workflow Removal .github/workflows/add-labels.yml	Removed the entire workflow file that automated adding the auto-merge label to pull requests labeled with scala-steward. The workflow triggered on PR events and conditionally created and applied the auto-merge label via GitHub CLI.
Auto-Merge Workflow Condition .github/workflows/auto-merge.yml	Added additional guard condition to the workflow job, restricting execution to only trigger when GitHub event state is success AND context equals continuous-integration/jenkins/branch, instead of running on any success state regardless of context.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly describes the main change: removing the add-labels GitHub workflow, which aligns with the primary modification in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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