Fix tests for turbopack support

[siddhsuresh]

Ensures the root context is read from the public API that webpack exposes. This is the first step for Turbopack support as Turbopack includes this.rootContext as well<!--
Thanks for opening a PR! Your contribution is much appreciated.
To make sure your PR is handled as smoothly as possible please:

• Link issue via "Closes #[issue_number]
• Choose & follow the right checklist for the change that you're making:

Please make sure to add a changeset. Run pnpm changeset in the root directory to do so.
Then select updated Blitz packages when prompted, and add a short message describing the changes.
The message should be user-facing — explain what was changed, not how.
Ignore if there are no user-facing changes.
-->

Closes: ?

What are the changes and their implications?

Bug Checklist

• Changeset added (run pnpm changeset in the root directory)
• Integration test added (see test docs if needed)

Feature Checklist

• Changeset added (run pnpm changeset in the root directory)
• Integration test added (see test docs if needed)
• Documentation added/updated (submit PR to blitzjs.com repo main branch)

[changeset-bot]

🦋 Changeset detected

Latest commit: f3d6e27

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 8 packages

Name	Type
blitz	Minor
@blitzjs/next	Major
@blitzjs/rpc	Major
next-blitz-auth	Patch
@blitzjs/auth	Major
@blitzjs/codemod	Major
@blitzjs/config	Major
@blitzjs/generator	Major

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR