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.

首先，使用包含 `uses: actions/checkout` 的 workflow 步驟重現 ctrl-click 行為，然後追蹤對未指定版本的連結處理。完成的標準是連結開啟 repository 主頁，而不是開啟包含 `tree/undefined` 的 URL；分別考慮擴充功能版本和醒目顯示最新版本的要求。

由索引模型根據 Issue 內容生成。