Link from a uses: with unspecified version goes to tree/undefined

**Describe the bug**
When writing `uses: actions/checkout` in a file, ctrl + clicking it to open in web browser opens it to github.com/actions/checkout/tree/undefined

**To Reproduce**
1. Create workflow with `uses: actions/checkout` in a step
2. ctrl + click it to go to github
3. 404 page as there is no undefined tag

**Expected behavior**
It should go to the repository main page

**Extension Version**
`v0.27.2`

**Additional context**
It would be cool to know the latest version of that module in the highlight.

Start by reproducing the ctrl-click behavior with a workflow step containing `uses: actions/checkout`, then trace the link handling for an unspecified version. Done means the link opens the repository main page rather than a URL containing `tree/undefined`; consider the extension version and the request for latest-version highlighting separately.

索引モデルが issue の本文から書いたものです。