ci: evaluate making GitHub lint checks required

[daviburg]

Problem

PR #252 restores the GitHub Lint workflow and proves the PowerShell, Markdown, and YAML jobs complete successfully. Those checks are currently advisory: the main ruleset requires connectors-sdk.public, but not the GitHub lint jobs. A red lint result can therefore be merged after approval if the required build remains green.

Proposed follow-up

After #252 merges and the check names are stable:

• Evaluate adding the PowerShell, Markdown, and YAML GitHub lint checks to the main ruleset.
• Confirm required-check names and strict update behavior using a test PR before enforcing them.
• Document whether Azure Pipelines remains the authoritative C# and package-validation gate.

This is a repository-governance change and should be coordinated with connectors-sdk-maintainers.

Follow-up from #252.