🐛 Use correct import path (#35286)
🐛 Use correct import path (#35286)

This was causing the `main` build [to fail](https://app.circleci.com/pipelines/github/ampproject/amphtml/13129/workflows/e28d6e95-6c29-4f46-8aad-61d917db82dd/jobs/210622).

```
extensions/amp-iframe/0.1/test/test-amp-iframe.js
  31:26  error  Unexpected use of file extension "js" for "../../../../testing/test-helper.js"  import/extensions
  31:26  error  Do not use relative path for aliased modules                                    module-resolver/use-alias
```

The original CI run for the PR did not catch this since it last ran before the aliased path change.
honeybadgerdontcare/amphtml,smartadserver/amphtml,alanorozco/amphtml,ampproject/amphtml,media-net/amphtml,media-net/amphtml,Gregable/amphtml,jpettitt/amphtml,honeybadgerdontcare/amphtml,jpettitt/amphtml,media-net/amphtml,danielrozenberg/amphtml,jpettitt/amphtml,alanorozco/amphtml,jridgewell/amphtml,jpettitt/amphtml,smartadserver/amphtml,alanorozco/amphtml,Gregable/amphtml,alanorozco/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,smartadserver/amphtml,mhc-gh/amphtml,jridgewell/amphtml,alanorozco/amphtml,Gregable/amphtml,honeybadgerdontcare/amphtml,honeybadgerdontcare/amphtml,jpettitt/amphtml,danielrozenberg/amphtml,Gregable/amphtml,danielrozenberg/amphtml,smartadserver/amphtml,Gregable/amphtml,ampproject/amphtml,ampproject/amphtml,mhc-gh/amphtml,smartadserver/amphtml,Gregable/amphtml,danielrozenberg/amphtml,Gregable/amphtml,honeybadgerdontcare/amphtml,media-net/amphtml,ampproject/amphtml,jridgewell/amphtml,jridgewell/amphtml,media-net/amphtml,mhc-gh/amphtml,jridgewell/amphtml,mhc-gh/amphtml,jridgewell/amphtml,smartadserver/amphtml,danielrozenberg/amphtml,jpettitt/amphtml,alanorozco/amphtml,jridgewell/amphtml,Gregable/amphtml,ampproject/amphtml,jpettitt/amphtml,ampproject/amphtml,mhc-gh/amphtml,ampproject/amphtml,alanorozco/amphtml,mhc-gh/amphtml,mhc-gh/amphtml,media-net/amphtml,mhc-gh/amphtml,ampproject/amphtml,honeybadgerdontcare/amphtml,honeybadgerdontcare/amphtml,danielrozenberg/amphtml,media-net/amphtml,danielrozenberg/amphtml,alanorozco/amphtml,media-net/amphtml