fix: $schema according to schemastore standards

[Vessel9817]

This is a petty change, I admit. This should not be a breaking change, by any means.

Since this repository has its schema hosted in Schemastore/schemastore, this change upholds the standards of schema drafting this repository widely follows. Namely, emphasis mine:

Valid schemas: ["https://json-schema.org/draft/2020-12/schema","https://json-schema.org/draft/2019-09/schema","http://json-schema.org/draft-07/schema#","http://json-schema.org/draft-06/schema#","http://json-schema.org/draft-04/schema#","http://json-schema.org/draft-03/schema#"]

Apologies for the inconvenience. Thanks for your time.

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