test(bank-redirect): add Giropay test context + fix Nexinets giropay config + add handler
- Fix Nexinets.js Giropay Response: change from requires_customer_action
to failed/error 12000 (matching actual API behavior)
- Add giropay case to Nexinets switch in redirectionHandler.js
(same selector as iDEAL: click Success link)
- Add Giropay test context to 18-BankRedirect.cy.js following EPS pattern
Co-Authored-By: Paperclip <noreply@paperclip.ing>