Add promotions route to Request validation list

Adds the PROMOTIONS_API constant to the route_list array in the Request class to allow promotions API calls to pass validation. This enables the GET /promotions, POST /promotions/{id}/activate, and POST /promotions/{id}/dismiss endpoints to function correctly.

Without this fix, all promotions API calls would fail with an "Invalid request api route" exception.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: dmallory42

includes/core/server/class-request.php

@@ -154,6 +154,7 @@ abstract class Request {
 		WC_Payments_API_Client::TERMINAL_READERS_API       => 'terminal/readers',
 		WC_Payments_API_Client::MINIMUM_RECURRING_AMOUNT_API => 'subscriptions/minimum_amount',
 		WC_Payments_API_Client::CAPITAL_API                => 'capital',
+		WC_Payments_API_Client::PROMOTIONS_API             => 'promotions',
 		WC_Payments_API_Client::WEBHOOK_FETCH_API          => 'webhook/failed_events',
 		WC_Payments_API_Client::DOCUMENTS_API              => 'documents',
 		WC_Payments_API_Client::VAT_API                    => 'vat',