[LOPS-1990] Fix fatal error on payment methods.

[kporras07]

Before:

Getting error when running terminus payment-method:list:

Fatal error: Declaration of Pantheon\Terminus\Collections\PaymentMethods::get($id): ?Pantheon\Terminus\Models\TerminusModel must be compatible with Pantheon\Terminus\Collections\TerminusCollection::get($id): Pantheon\Terminus\Models\TerminusModel in phar:///opt/homebrew/Cellar/terminus/3.3.0/bin/terminus/src/Collections/PaymentMethods.php on line 39

The second commit addresses the following message:

terminus payment-method:list
 [warning] Model data missing for 0
 [warning] There are no payment methods attached to this account.
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  Label   ID
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