"Context access might be invalid: workspace"

**Describe the bug**

If a workflow YAML has `${{runner.workspace}}` value for the key [`jobs..steps[*].working-directory`](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsworking-directory) it triggers the warning in the issue description.

**To Reproduce**

```yml
- name: Test
working-directory: ${{runner.workspace}}/OpenCL-Headers/build
```

**Expected behavior**

No warning.

**Screenshots**


**Extension Version**

`v0.26.2`

**Additional context**

None.

首先，使用提供的 workflow YAML 重现该警告，并跟踪 jobs.\u003cjob_id\u003e.steps[*].working-directory 包含 runner.workspace 时的验证过程。将该行为与文档中说明的 working-directory 语法进行比较；完成标准是示例不产生警告，同时不削弱对其他无效上下文的验证。

由索引模型根据 Issue 内容生成。