enforce explanation for necessary nolints and fix bugs (#34883)

Follows up https://github.com/go-gitea/gitea/pull/34851

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/optional/serialization_test.go

@@ -4,7 +4,7 @@
 package optional_test
 
 import (
-	std_json "encoding/json" //nolint:depguard
+	std_json "encoding/json" //nolint:depguard // for testing purpose
 	"testing"
 
 	"code.gitea.io/gitea/modules/json"