forward and backward mouse buttons are recognized as middle mouse button

Steps to reproduce:

1. create new project and add input system package

2. connect a mouse with 5 buttons

3. open input debugger and press forward/backward buttons

Actual results: both trigger middle mouse button

Expected results: they trigger forward and backward button

Reproducible with versions: 1.8.1

Not reproducible with versions: n/a

Can’t test with versions: n/a

Tested on (OS): macOS 14

Notes:

• works well on Windows