Add type check

[ylemkimon]

https://github.com/actions/github-script/blob/fc4d6279013dd0c4f4db0c7c21ff1a1c46e5c8ea/src/async-function.ts#L1-L14:

import * as core from '@actions/core'
import {Context} from '@actions/github/lib/context'
import {GitHub} from '@actions/github/lib/utils'
import * as io from '@actions/io'

const AsyncFunction = Object.getPrototypeOf(async () => null).constructor

type AsyncFunctionArguments = {
  context: Context
  core: typeof core
  github: InstanceType<typeof GitHub>
  io: typeof io
  require: NodeRequire
}