fix: include yarn.lock in preview build artifacts

[cryptodev-2s]

Explanation

The publish-preview job fails because yarn workspaces foreach can't resolve the renamed @metamask-previews/ packages. The root cause is that prepare-preview-builds.sh updates the lockfile via yarn install --no-immutable, but yarn.lock is not included in the uploaded artifacts. The publish job gets a stale lockfile from main that doesn't match the renamed package names.

This adds yarn.lock to the artifact upload and removes the path override on download so it extracts to the workspace root alongside packages/.

References

• Fixes failure introduced in chore: secure PUBLISH_PREVIEW_NPM_TOKEN with GitHub environment #8011

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
CI workflow-only change that affects artifact packaging/restoration; low risk outside of potentially impacting preview publish reliability.

Overview
Fixes the preview publish workflow by including the updated yarn.lock in the uploaded build artifact set, ensuring the publish job uses the same lockfile produced by yarn prepare-preview-builds.

Also removes the actions/download-artifact path override so artifacts (including yarn.lock) restore to the workspace root instead of being extracted under packages/.

^{Written by Cursor Bugbot for commit 0a45543. This will update automatically on new commits. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

[Gudahtt]

This is the error in question I'm guessing? https://github.com/MetaMask/core/actions/runs/22324841398/job/64592901687

I'm not following why this change would fix this error. Is it possible that the problem is that the lockfile is not cached along with the build output?

[Gudahtt]

LGTM!