fix(GHES): respect GITHUB_API_URL when creating installation access token (#38)

Follow up to #36. I just wanted to do some refactoring but turns out I
missed to pass the custom `request` instance to `createAppAuth`. It will
fallback to the default `request` which does not respect
`GITHUB_API_URL`

lib/post.js

@@ -1,11 +1,8 @@
 // @ts-check
 
-import core from "@actions/core";
-import { request } from "@octokit/request";
-
 /**
- * @param {core} core
- * @param {request} request
+ * @param {import("@actions/core")} core
+ * @param {import("@octokit/request").request} request
  */
 export async function post(core, request) {
   const token = core.getState("token");