fixed php8.1 float precision loss notice

[leonardola]

Part of https://github.com/Automattic/woocommerce-payments/issues/5985

Description

This PR fixes a notice generated by php 8.1 about precision loss on a division by 2 for an integer parameter.

How to test this PR

• Using php 8.1
• Checkout this branch
• Open /wp-admin
• No error/warning should show up or be logged

Product impact

• [x] Added changelog entry (or does not apply)

[Jinksi]

Thanks @leonardola @alefesouza 🙌