Migrate to ESM (#484)

* Migrate to ESM

* just use `require.resolve`

* reuse setup action

* checkout PR head for a sec

* ls things

* try a thing

* the dirname had a trailing whitespace, lol

src/git.ts

@@ -2,7 +2,7 @@ import * as core from "@actions/core";
 import { exec, getExecOutput } from "@actions/exec";
 import * as github from "@actions/github";
 import { commitChangesFromRepo } from "@changesets/ghcommit/git";
-import { Octokit } from "./octokit";
+import type { Octokit } from "./octokit.ts";
 
 type GitOptions = {
   cwd: string;