Refuse @jekyllbot: merge when Release Please workflow is present on the PR base branch

[Copilot]

Jekyll uses Release Please instead of the legacy jekyllbot merge flow, so merge-command comments should not execute in that mode. This update makes merge handling resilient by detecting Release Please on the PR’s base branch and responding with guidance instead of merging.

• Release-Please-aware merge gate

  • MergeAndLabel now reads PR metadata first and checks for .github/workflows/release-please.yml on pr.base.ref.
  • If present, the handler exits early and does not call PullRequests.Merge.

• User-facing refusal response

  • Added a dedicated refusal reply posted to the PR thread when @jekyllbot: merge is used in a Release Please repo.
  • Reply points maintainers to the merge documentation URL.

• Targeted implementation additions

  • Added hasReleasePleaseWorkflowOnBranch(...) to check workflow-file existence via Repositories.GetContents.
  • Added replyWithReleasePleaseMergeRefusal(...) to centralize refusal comment behavior.

releasePleaseEnabled, err := hasReleasePleaseWorkflowOnBranch(context, owner, repo, prInfo.GetBase().GetRef())
if err != nil { return context.NewError(...) }

if releasePleaseEnabled {
	if err := replyWithReleasePleaseMergeRefusal(context, owner, repo, number); err != nil {
		return context.NewError(...)
	}
	return nil
}