JSON schema for useFlatConfig can be more specific

[predragnikolic]

The default value for useFlatConfig is specified as null,
but the type was specified as boolean.

vscode-eslint/package.json

Line 189 in 7b17139

"default": null,

which makes LSP-json complain a bit...

Would it be better to specify a bool value as a default,
or leave it as is?

[dbaeumer]

The reason for not having a bool is that the default changes with ESLint versions. I will fix the schema to make null a valid value.