is.array narrows the value to a *readonly* array

[aleclarson]

It should only do that for type unions that contain a readonly T[] type.

import { is } from '@alloc/is'

declare const a1: any
declare const a2: string | readonly string[]
declare const a3: string | string[]

is.array(a1) // => any[]
is.array(a2) // => readonly string[]
is.array(a3) // => string[]