Failure reproduction: add test for @ember/string @ 4

[NullVoxPopuli]

Based on errors I'm seeing related to ember-cli-deprecation-workflow, I have a hunch that something is related to implicit modules.

In ember-cli/ember-cli-deprecation-workflow#194 we think that @ember/string should be able to be removed from ember-cli-deprecation-workflow entirely, as it's not imported anywhere.
(Update: tests seem to agree: ember-cli/ember-cli-deprecation-workflow#197 )

---

We do try to account for real @ember/string here: https://github.com/embroider-build/embroider/blob/main/packages/shared-internals/src/ember-standard-modules.ts#L26-L27

[NullVoxPopuli]

The types of errors:

Module not found: Error: 
  ember-cli-app-version is trying to import the app's @ember/string package, 
  but it seems to be missing

and

Could not find module `@ember/string` 
  imported from `(require)` at http://localhost:7357/assets/vendor.js, line 253\

🤔