Message actions aren't working

[shaydewael]

Description

Message actions aren't handled properly, so the Could not determine the type of an incoming event. No listeners will be called. error is logged.

I believe this is due to https://github.com/slackapi/bolt/blob/master/src/helpers.ts#L49 since message actions won't have an actions array or be type dialog_submission.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.