> Conforming to a complex specification is not inherently a good thing
Kind of a hard disagree here; if you don't want to conform to a specification, don't claim that you're accepting documents from that specification. Call it github-flavored YAML (GFY) or something and accept a different file extension.
https://github.com/actions/runner/issues/1182
> YAML 1.1 to be an important goal: they still don't support merge keys
right, they don't do merge keys because it's not in YAML 1.2 anymore. Anchors are, however. They haven't said that noncompliance with YAML 1.2 spec is intentional