### Godot version

4.0 beta 17

### System information

Windows 10

### Issue description

Setting the color attribute in ParticleProcessMaterial for GPUParticles2D does not work with compatibility renderer
(works with forward+)

### Steps to reproduce

Set renderer to compatibility
Create a GPUParticles2D
Add ParticleProcessMaterial and set Color attribute (creating a particle shader and setting the `COLOR` is the same)


### Minimal reproduction project

[Particle2DColor.zip](https://github.com/godotengine/godot/files/10678236/Particle2DColor.zip)

src_rect.size.x *= -1;
						state.instance_data_array[r_index].flags |= FLAGS_FLIP_H;
					}
					if (rect->flags & CANVAS_RECT_FLIP_V) {
						src_rect.size.y *= -1;
						state.instance_data_array[r_index].flags |= FLAGS_FLIP_V;
					}
					if (rect->flags & CANVAS_RECT_TRANSPOSE) {
						state.instance_data_array[r_index].flags |= FLAGS_TRANSPOSE_RECT;
					}
					if (rect->flags & CANVAS_RECT_CLIP_UV) {
						state.instance_data_array[r_index].flags |= FLAGS_CLIP_RECT_UV;
					}
				} else {
					dst_rect = Rect2(rect->rect.position, rect->rect.size);
					if (dst_rect.size.width < 0) {
						dst_rect.position.x += dst_rect.size.width;
						dst_rect.size.width *= -1;
					}
					if (dst_rect.size.height < 0) {
						dst_rect.position.y += dst_rect.size.height;
						dst_rect.size.height *= -1;
					}
					src_rect = Rect2(0, 0, 1, 1);
				}
				if (rect->flags & CANVAS_RECT_MSDF) {
					state.instance_data_array[r_index].flags |= FLAGS_USE_MSDF;
					state.instance_data_array[r_index].msdf[0] = rect->px_range; 
					state.instance_data_array[r_index].msdf[1] = rect->outline; 
					state.instance_data_array[r_index].msdf[2] = 0.f;