Fallback to `select` if array of `checkboxes` fail

Allows fields that are arrays of strings to be passed to `<select multiple>`
inputs.
So does that mean `#fill` becomes:

```ruby
if has_multi_select?
  value.each { |option| select option, from: label }
else
  fill_checkboxes_or_raise!
end
```

With `fill_checkboxes_or_raise` handling the `Capybara` rescue and `Formulaic` rethrow?