Sprite 'modulate' property affects siblings when Batching is enabled

[tsuinex]

Godot version:
3.3.stable.official

OS/device including version:
OpenGL ES 3.0 Renderer: AMD Radeon HD 8800M Series (VERDE, DRM 3.40.0, 5.11.10-1-MANJARO, LLVM 11.1.0)

Issue description:
I have an enemy sprite that turns red using the self_modulate property when it is hit. After upgrading to Godot 3.3, this red tint also sometimes applies to the player character, which is an unrelated node in the scene tree.

I expected the 'self_modulate' property to affect only the selected node (and its children in the case of the 'modulate' property).

Steps to reproduce:
I'm not certain whether all these steps are necessary, but:

1. Create a 2D scene, add a TileMap node as a child, and populate it with some tiles.
2. Create a sprite, set its 'modulate' or 'self_modulate' property to a distinct colour, and move this sprite beyond the top-left of the origin (0,0).
3. Create another sprite, and give it a Light2D child with a texture. This sprite will now be tinted the same colour as the other sprite.

The problem also occurs when running the project, but is dependant on the positions of the sprites, so it doesn't trigger in the same situation. In my game, it happens on and off as I and the enemy move around, and flickers when I enable Flash Batching, which shows that it is an issue related to the new batching feature.

Minimal reproduction project:
modulate_bug.zip

[lawnjelly]

It seems related to the light joining. When I set rendering/batching/lights/max_join_items to 0 it cures it. It also doesn't need to be a tilemap, I replaced it with a sprite and it still occurs.

It may be a case where I need to prevent light joining.

[lawnjelly]

Got it, there's no need to prevent light joining which is good.

There's a bit where it reapplies the final_modulate for an item during the lighting pass. The only thing is, for joined items (non single items) we don't want to do this as the modulates are baked. I have it working, but want to check it a bit more before making a PR as the light passes isn't fresh in my mind.

[akien-mga]

Fixed by #48151.