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

.github/workflows/version-or-publish.yml

@@ -11,16 +11,8 @@ jobs:
   changesets:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout Repo
-        uses: actions/checkout@v4
-
-      - name: Use Node.js 20
-        uses: actions/setup-node@v4
-        with:
-          node-version: 20.x
-
-      - name: Install Dependencies
-        run: yarn --frozen-lockfile
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/ci-setup
 
       - name: Build
         run: yarn build