Fixed using move_and_slide with stop_on_slope stopping too early

[Piet-G]

This makes it stop exactly on the slope, I'm not 100% sure if this if this is the correct fix let me know what you think.

Fixes #23675

[akien-mga]

13:55 <reduz> the fix could actually work
13:55 <reduz> it's pretty smart
13:56 <reduz> not sure if it will have side effects
13:56 <reduz> but it's well thought
13:56 <reduz> i would merge and see what happens

[akien-mga]

Thanks!