Fix form params for testEventPaymentForms

[mattwire]

Overview

This test should be setting payment_processor_id and not processor_id for the ID of the payment processor when building the form.

Before

Wrong parameter being set.

After

Right parameter being set.

Technical Details

With the existing eventcart it doesn't actually matter because the parameter is not used but it does matter for #17886

Comments

[civibot]

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[seamuslee001]

Test only fix merging