Pets can only have one approved application on them at any time

[aspeth]

As a visitor
When a pet has an "Approved" application on them
And when the pet has a "Pending" application on them
And I visit the admin application show page for the pending application
Then next to the pet I do not see a button to approve them
And instead I see a message that this pet has been approved for adoption
And I do see a button to reject them