Apply available credit to any at-booking charge, not just scheduled

A payer's account credit should offset any charge raised at booking, so
drop the scheduled-only guard. Covers the one-time pay-now flow too.

Co-authored-by: anthropic/claude-opus-4-8

src/Booking/LessonBooker.php

@@ -196,8 +196,8 @@ class LessonBooker {
 				payerId: $payerId
 			);
 
-			// Apply any available credit to a scheduled charge raised at booking.
-			if ( $offering->isScheduledBilling() && null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
+			// Apply any available credit to a charge raised at booking.
+			if ( null !== $payment && null !== $payment->id && Payment::STATUS_PENDING === $payment->status ) {
 				$this->payments->applyCredits( $payerId, [ $payment ] );
 				$payment = $this->payments->findPayment( (int) $payment->id ) ?? $payment;
 			}