ViewportTexture doesn't update when used as a Light3D projector texture

[betalars]

Godot version

4.0 release

System information

nixos-unstable

Issue description

See this Video on YouTube illustrating it

• the Viewport Texture when set as a projector in a spotlight will sometimes render random video memory artefacts
• the texture will not update, even when the viewport changes (Sorry I don't know why I called it cookie)

  Steps to reproduce

1. Add a Spot light, Configure it to use a projected texture
2. Create a sub-viewport and put something into it that moves
3. set the Viewport to always update
4. Assign a Viewport Texture and choose the created Viewport

OBSERVED: Sometimes the projector image does not update, sometimes iit will just show GPU Memory Glitches EXPECTED: the cookie shows what's happening in the viewport

Minimal reproduction project

Minimal Steps to Reproduce minimal-lighting-cookie.zip

[betalars]

probably related to #73400

[AThousandShips]

What is a lighting cookie?

[betalars]

What is a lighting cookie?

I have not the slightest idea where my brain took that name.

Obviously, i meant to refer to the texture you can put as a projector, as demonstrated in the video.

[clayjohn]

Since the buggy part of this report is the same as https://github.com/godotengine/godot/issues/74353, I have renamed this to be more clear that it is for a discussion of having the ViewportTexture update when used as a projector texture. This is the same root problem as https://github.com/godotengine/godot/issues/73400, just with projector textures instead of decals