VSCode not validating sample

Extension sample

language-configuration.json

VS Code version

1.107.0

What went wrong?

VSCode is showing a squiggly line on the comments.lineComment property which I have set to "//" in my language-configuration.json file.

Incorrect type. Expected "object".

It seems to match the schema as defined in the docs, but I can't find the actual JSON schema anywhere to see why it doesn't match. Here's the full contents of my language-configuration.json:

{
  "comments": {
    "lineComment": "//"
  },
  "brackets": [
    ["{", "}"],
    ["(", ")"]
  ],
  "autoClosingPairs": [
    { "open": "{", "close": "}" },
    { "open": "(", "close": ")" }
  ],
  "surroundingPairs": [
    ["{", "}"],
    ["(", ")"]
  ]
}

Is the JSON schema for this file published anywhere? Is the documentation wrong?