Add YAML Linting to validate changes to workflows

The generator workflow and various configuration files in .github use YAML configuration. In most cases, syntax errors in these YAML configurations will not be detected through existing PR checks. Add a linter to catch basic errors.

Inspect the generator workflow and YAML configuration files under .github, then review the existing pull-request checks to see where validation is configured. Identify a linter that can validate these YAML files and integrate it so syntax errors fail checks; done means malformed workflow or configuration YAML is caught by PR checks.

Written by the indexing model from the issue text.