Use native ESM for dev scripts (#12296)

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

test/esm/index.js

@@ -1,6 +1,6 @@
-import babelRuntimeTestcases from "./babel-runtime.mjs";
-import babelRuntimeCorejs3Testcases from "./babel-runtime-corejs3.mjs";
-import testRunner from "./test-runner.mjs";
+import babelRuntimeTestcases from "./babel-runtime.js";
+import babelRuntimeCorejs3Testcases from "./babel-runtime-corejs3.js";
+import testRunner from "./test-runner.js";
 
 (async () => {
   await testRunner(babelRuntimeTestcases);

test/esm/package.json

@@ -2,7 +2,7 @@
   "name": "@babel/test-esm",
   "private": true,
   "type": "module",
-  "exports": "./index.mjs",
+  "exports": "./index.js",
   "devDependencies": {
     "@babel/runtime": "workspace:*",
     "@babel/runtime-corejs3": "workspace:*",