Upgrading from `@actions/github` V5 -> V6 caused TypeErrors within `getOcktokit()`

Wasn't entirely sure if this issue belonged here or plugin-rest-endpoint-methods.js as the error was emitting from plugin-rest-endpoint-methods.js: https://github.com/octokit/plugin-rest-endpoint-methods.js/issues/683.

What happened?

Version 5 of @actions/github, I was able to do this within my tests:

import { getOctokit } from '@actions/github'
import type { Endpoints } from '@octokit/types'
import sinon from 'sinon'

const octokit = getOctokit('token')

const stubLabelList = () => {
	return sinon.stub(octokit.rest.issues, 'listLabelsForRepo').resolves({
		data: [MOCK_LIST_LABELS],
		status: 200
		} as Endpoints["GET /repos/{owner}/{repo}/labels"]["response"])
	}
}

const github = {
	getOctokit: () => octokit
}

// pass github to other test functions etc 

As of version 6, I've had to do something like:

import { getOctokit } from '@actions/github'
import type { Endpoints } from '@octokit/types'
import sinon from 'sinon'

const octokit = getOctokit('token')

const github = {
	getOctokit: () => {
		...octokit, 
		rest: { 
			issues: {
				listLabelsForRepo: () => {
					return {
						data: [MOCK_LIST_LABELS],
						status: 200
					} as Endpoints["GET /repos/{owner}/{repo}/labels"]["response"])
				}
			}
		} 
	}
}

I noticed this was a change in way the endpoints are generated and is now done via a proxy as of https://github.com/octokit/plugin-rest-endpoint-methods.js/pull/622, could this of introduced unwanted side effects or is this the intended behaviour?

Versions

@actions/github: v6
NodeJS: 18

Relevant log output

TypeError: Cannot destructure property ‘decorations’ of ‘endpointMethodsMap.get(...).get(...)’ as it is undefined.

Start at getOctokit in @actions/github and the proxy-based endpoint generation in plugin-rest-endpoint-methods.js, then compare the v5 and v6 behavior with plugin pull request 622 and issue 683. Reproduce the TypeError while stubbing listLabelsForRepo; done means determining whether the proxy causes the regression and resolving or documenting the changed behavior.