Add `assert { type: "json" }` to json import

[haohanyang]

I ran into the error ERR_IMPORT_ASSERTION_TYPE_MISSING when running npm run build (node version v18.17.1). Adding assert { type: "json" } seems to fix it.

Ref: https://stackoverflow.com/questions/70106880/err-import-assertion-type-missing-for-import-of-json-file