[NFC] Convert Payment Processor ID field to payment processor in even…

[seamuslee001]

…t create in tests

Overview

@eileenmcnaughton what I found was that you were passing in the key of payment_processor_id https://github.com/civicrm/civicrm-core/blob/master/tests/phpunit/CRM/Event/Form/Registration/ConfirmTest.php#L475 when the field name in this case is payment_processor and it expects an array to be passed in not a string so was figured this is the easiest place to handle it

Before

testOnlineRegNoPrice test fails on notice error in php8.1

After

Test passes in php8.1

ping @eileenmcnaughton @demeritcowboy

[civibot]

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