Required property is missing: shell

[ghost]

Describe the bug

The VS Code extension lacks critical linting support. Specifically, when creating a Composite Action, it fails to provide a warning that providing a shell property is required. I only became aware of this after pushing the update and encountering the following error:

.github/actions/aws-config/action.yml (Line: 18, Col: 7): Required property is missing: shell

To Reproduce
Steps to reproduce the behavior:

1. With this workflow '...'
2. Do this '...'
3. See error

Expected behavior
VS Code extension shows a warning when authoring a Composite Action if the shell property isn't specified.

Screenshots
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Extension Version
v1.x.y

Additional context
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