Add missing line to use_field_init_shorthand "true" example

[mqudsi]

The last declaration (let b = ...) is where all the difference between the
"false" and "true" cases lies, but it was omitted from the "true" example for
unknown reasons.

Assuming it was by accident, this patch adds the last line from the "false"
example to the "true" example, formatted as it would have been with
use_field_init_shorthand = true.

[calebcartwright]

Thanks but I'm going to close for the reasons discussed in #5522 (comment) as I want to avoid any additional toggling we've been doing in the existing config snippet structure (we've done this a bit but almost always find what seems more clear to one person actually muddies things for someone else)

[mqudsi]

Ok, thanks.