Open action on GitHub link is broken without action version

[timokoessler]

Describe the bug
If you use the GitHub Actions VSCode extension and click on a action without a version, the url opened in the browser contains undefined.

To Reproduce
Steps to reproduce the behavior:

1. Install the GitHub Actions for VS Code plugin
2. Open a workflow file
3. Remove the version number from a action, e.g. uses: actions/checkout
4. Click "Open action on GitHub"
5. It opens https://github.com/actions/checkout/tree/undefined/

Expected behavior
Opens https://github.com/actions/checkout/ in the browser.

Package/Area

• Expressions
• Workflow Parser
• Language Service
• Language Server

Package Version
v0.3.13

Additional context
As a user I want to click on a action link without a version to check what is the latest available version of this action.