custom config file doesn't appear to await async config functions

[fridaystreet]

Describe the bug

using an async function for the config skips using the config and just uses the built in config

custom:
  esbuild:
    config: './esbuild.config.js'

with

module.exports=async (serverless) => {

  await someAsyncFunction()

  return {
    ...the config
  }

To Reproduce

as above

Expected behavior
The call to the config function waits for it to fulfill the promise and return the config

Versions (please complete the following information):

• OS: Mac
• Serverless Framework Version: 4.4.7
• Plugin Version: 1.54.5