Add function to return proxy agent dispatcher for compatibility with latest octokit

packages/http-client/__tests__/proxy.test.ts

@@ -3,6 +3,7 @@
 import * as http from 'http'
 import * as httpm from '../lib/'
 import * as pm from '../lib/proxy'
+import { ProxyAgent } from "undici";
 // eslint-disable-next-line @typescript-eslint/no-var-requires, @typescript-eslint/no-require-imports
 const proxy = require('proxy')
 
@@ -13,7 +14,7 @@ const _proxyUrl = 'http://127.0.0.1:8080'
 describe('proxy', () => {
   beforeAll(async () => {
     // Start proxy server
-    _proxyServer = proxy()
+    _proxyServer = proxy.createProxy()
     await new Promise<void>(resolve => {
       const port = Number(_proxyUrl.split(':')[2])
       _proxyServer.listen(port, () => resolve())
@@ -294,6 +295,15 @@ describe('proxy', () => {
     expect(agent.proxyOptions.port).toBe('8080')
     expect(agent.proxyOptions.proxyAuth).toBe('user:password')
   })
+
+  it('ProxyAgent is returned when proxy setting are provided', async () => {
+    process.env['https_proxy'] = 'http://127.0.0.1:8080'
+    const httpClient = new httpm.HttpClient()
+    const agent = httpClient.getAgentDispatcher('https://some-url')
+    // eslint-disable-next-line no-console
+    console.log(agent)
+    expect(agent instanceof ProxyAgent).toBe(true)
+  })
 })
 
 function _clearVars(): void {