Fix assign with swizzle in shader not doing varying validation check

servers/rendering/shader_language.cpp

@@ -4639,6 +4639,10 @@ bool ShaderLanguage::_validate_assign(Node *p_node, const FunctionInfo &p_functi
 			return false;
 		}
 
+		if (shader->varyings.has(var->name)) {
+			return _validate_varying_assign(shader->varyings[var->name], r_message);
+		}
+
 		if (!(p_function_info.built_ins.has(var->name) && p_function_info.built_ins[var->name].constant)) {
 			return true;
 		}