### 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)

case Item::Command::TYPE_MESH:
		case Item::Command::TYPE_MULTIMESH:
		case Item::Command::TYPE_PARTICLES: {
			GLES3::MeshStorage *mesh_storage = GLES3::MeshStorage::get_singleton();
			GLES3::ParticlesStorage *particles_storage = GLES3::ParticlesStorage::get_singleton();
			RID mesh;
			RID mesh_instance;
			uint32_t instance_count = 1;
			GLuint instance_buffer = 0;
			uint32_t instance_stride = 0;
			uint32_t instance_color_offset = 0;
			bool instance_uses_color = false;
			bool instance_uses_custom_data = false;
			if (state.canvas_instance_batches[p_index].command_type == Item::Command::TYPE_MESH) {
				const Item::CommandMesh *m = static_cast<const Item::CommandMesh *>(state.canvas_instance_batches[p_index].command);
				mesh = m->mesh;
				mesh_instance = m->mesh_instance;
			} else if (state.canvas_instance_batches[p_index].command_type == Item::Command::TYPE_MULTIMESH) {
				const Item::CommandMultiMesh *mm = static_cast<const Item::CommandMultiMesh *>(state.canvas_instance_batches[p_index].command);
				RID multimesh = mm->multimesh;
				mesh = mesh_storage->multimesh_get_mesh(multimesh);
				if (mesh_storage->multimesh_get_transform_format(multimesh) != RS::MULTIMESH_TRANSFORM_2D) {
					break;
				}
				instance_count = mesh_storage->multimesh_get_instances_to_draw(multimesh);
				if (instance_count == 0) {
					break;
				}
				instance_buffer = mesh_storage->multimesh_get_gl_buffer(multimesh);
				instance_stride = mesh_storage->multimesh_get_stride(multimesh);