"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.

Start by reproducing the warning with the provided workflow YAML and trace the validation for jobs..steps[*].working-directory when it contains runner.workspace. Compare that behavior with the documented working-directory syntax; done means the example produces no warning without weakening validation for other invalid contexts.

索引モデルが issue の本文から書いたものです。