This makes it easier to create helper functions like:
```ts
function createReporter(options: MyOptions) {
return ['my-reporter', options] as const
}
```
At the moment, such functions can't be passed to `reporters` because a
readonly array is not assignable to the expected mutable array.
Playwirght certainly doesn't require those arrays to be mutable so it
would make sense to relax this.
82aefd24db