Treat `flake.lock` files as JSON (#13886)

This PR updates the default settings to treat Nix's `flake.lock` files
as JSON.

Resolves https://github.com/zed-extensions/nix/issues/2.

Release Notes:

- Nix's `flake.lock` files are now automatically identified as JSON.
c190ed49daMarshall Bowers committed on 7/5/2024, 9:17:27 PM· committed by GitHubparent5c7e6b7
1 file changedLine totals unavailable