fix(ci): checkout full PR ref

[subeax]

Summary

Pass the full github.ref to the reusable test workflow instead of github.ref_name.

For pull requests, github.ref_name is <number>/merge. Checkout interprets that value as refs/heads/<number>/merge, which does not exist. The full ref preserves GitHub's actual refs/pull/<number>/merge path.

Testing

• confirmed PR feat(macos): support Network Extension VPNs #37's standalone Test workflow passes
• confirmed its Build workflow fails only while fetching refs/heads/37/merge
• verified the workflow diff and whitespace

Refs #37

• Have you tested the code?
• Have you checked that the existing tests are passing?
• The destination branch is develop