Option to turn off schema enforcement for a single document via modeline

Is your enhancement related to a problem? Please describe.

I have a YAML document in a format for which no accurate schema exists. (This is a Concourse pipeline, but https://github.com/cappyzawa/concourse-pipeline-jsonschema has some bugs with current Concourse releases).

When I don't specify any schema, the first element of my document has errors flagged: "Property resource_types is not allowed"; "Incorrect type. Expected one of array, null."

I don't know what the document is being compared against -- as there's no modeline specifying a type, I would have expected there to be no schema-based validation at all.

It's unclear to me whether turning off validation altogether also prevents validation for well-formedness; not knowing this, I'm hesitant to take that step.

Note that I use Helix, not VS Code.

Describe the solution you would like

It should be possible to specify something like # yaml-language-server: $schema=none to prevent any schema validation from taking place.

Describe alternatives you have considered

I have considered turning off validation altogether via global configuration.

Additional context

No files or tests are named in the issue. Begin by locating modeline handling and schema-validation paths, then check existing validation tests; done should mean a document-level modeline can disable schema validation without disabling well-formedness checks.