Reusable workflows can be referenced locally

**Describe the bug**

According to the blog post, [Reusable workflows can be referenced locally](https://github.blog/changelog/2022-01-25-github-actions-reusable-workflows-can-be-referenced-locally/), however VS Code extension does not support it yet, and instead complains about the lack of `@{ref}` part.

**To Reproduce**
Steps to reproduce the behavior:
1. With this simple workflow:
```yml
jobs:
build:
name: Build
runs-on: ubuntu-latest

steps:
- uses: '.github/workflows/reusable-build.yml'
```
3. See error

It doesn't matter whether the reusable file `reusable-build.yml` actually exists.

**Expected behavior**

`@{ref}` part should be optional.

**Screenshots**

**Extension Version**

`v0.31.0`

**Additional context**

Bonus bug: tree/**undefined** in the ctrl+click URL leads to a Not Found page.

Start with the provided workflow reproducer and trace the VS Code extension's validation of the `uses` value. Confirm that a local `.github/workflows/reusable-build.yml` reference is accepted without an `@{ref}` suffix, and check the ctrl+click URL behavior for the reported `tree/undefined` case. Done means the error is removed for valid local references and navigation no longer produces that URL.

Scritto dal modello di indicizzazione a partire dal testo della issue.