2D Platformer Demo: bullet fall through the floor

[xalerthur]

Which demo project is affected:
2D Platformer Demo (KinematicBody)

Issue description:
Bullet fall through the floor (see video below from 5th second).

Platformer2D-2023-07-07_12.43.34.mp4

[xalerthur]

And not only through floor...

Platformer2D-2023-07-07_13.05.25.mp4

[Calinou]

This demo is being remade entirely in #922, which may fix the issue. You can also check the original 3.x version of the new demo here: https://github.com/godotengine/godot-demo-projects/tree/3.x/2d/platformer