make LIGHT_UV constant

servers/visual/shader_types.cpp

@@ -229,7 +229,7 @@ ShaderTypes::ShaderTypes() {
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT_VEC"] = ShaderLanguage::TYPE_VEC2;
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT_HEIGHT"] = ShaderLanguage::TYPE_FLOAT;
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT_COLOR"] = ShaderLanguage::TYPE_VEC4;
-	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT_UV"] = ShaderLanguage::TYPE_VEC2;
+	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT_UV"] = constt(ShaderLanguage::TYPE_VEC2);
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["LIGHT"] = ShaderLanguage::TYPE_VEC4;
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["SHADOW_COLOR"] = ShaderLanguage::TYPE_VEC4;
 	shader_modes[VS::SHADER_CANVAS_ITEM].functions["light"].built_ins["POINT_COORD"] = constt(ShaderLanguage::TYPE_VEC2);