Can you support merge_group event in plan-preview-action ?

[TakumaKurosawa]

What would you like to be added:

I would like you to support the merge_group event in plan-preview-action.

Why is this needed:

My project is using merge queue.

Merge queue is failed with this error:

unexpected event merge_group, only "pull_request", "issue_comment" and "push" event are supported

Reference:

pipecd/tool/actions-plan-preview/main.go

Lines 231 to 233 in 7b471d7

	func isSupportedGitHubEvent(event string) bool {
	return event == pullRequestEventName || event == commentEventName || event == pushEventName
	}