fix: update JSON of pet carrier items with correct property

[chaosvolt]

Purpose of change

Turns out #4713 also changed a properly in the JSON for pet carrier iuse for some wacky reason.

Describe the solution

Updated pet carrier items to use creature_size_capacity instead of monster_size_capacity, in both vanilla items and in mods (one result in Aftershock was found).

Describe alternatives you've considered

Changing the string back to monster_size_capacity because I have no goddamn idea why someone would ever make such a pointlessly minor change that does nothing but require the JSON to be updated, let alone why it got included in an accessibility port.

Testing

1. Checked affected files for syntax and lint errors.
2. Load-tested in compiled test build.
3. Scooped up a dog in a pet carrier, it works as expected.

Additional context

Checklist

[KheirFerrum]

Confirmed issue, confirmed solution. Should be good to merge.