Only bundle the release build, and don't import src in tests (#13978)

* Only bundle the release build, and don't import `src` in tests

* Use file extension to signal skipping

* Remove unnecessary config change

* Fix imports

packages/babel-plugin-proposal-optional-chaining/test/util.skip-bundled.js

@@ -1,4 +1,4 @@
-import { willPathCastToBoolean } from "../src/util.js";
+import { willPathCastToBoolean } from "../lib/util.js";
 import { parseSync, traverse } from "@babel/core";
 
 function getPath(input, parserOpts) {