test: add (failing) test for 2d fluids

[benthillerkus]

It seems fluid collisions broke recently and the test suite couldn't catch it

[Ughuuu]

odd, the tests seem to crash with godot crashing on cicd..

/home/runner/work/_temp/7b7826ce-9114-4f99-bd78-b5c4dd0c91a6.sh: line 3: 5035 Aborted (core dumped) "$GODOT4" --headless --path ./bin2d --import 2>&1

I wonder if it was like this for a while or if its new, will investigate anyway. Thx for contribution. This test you changed, I need to also check visually, so will do that and then merge if good.

[Ughuuu]

Actually, on mac the tests pass, minus the 1 regression. Are you sure you added the test to the test suite?

    1 Regression(s):
        1. Faucet2D | testing collision > Fluid particles stay above the collision height

    6 Improvement(s):
        1. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in x with CCD Ray does not pass through the wall
        2. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in x with CCD Cast shape does not pass through the wall
        3. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in y with CCD Cast shape does not pass through the wall
        4. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in x with CCD Ray does not pass through the wall
        5. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in x with CCD Cast shape does not pass through the wall
        6. RigidBody2D | testing Continuous Collision Detection (CCD) > Rigid moving in y with CCD Cast shape does not pass through the wall

[benthillerkus]

The issue with fluid physics I'm running into on the current version is that collisions seem to be ignored, so that's the regression test I've added.
I haven't had any issues with crashing (though I only tested on Windows).