ci/cd: migrate backend linter to v2. fixed unit test workflow (#400)

backend/internal/middleware/cors.go

@@ -1,6 +1,8 @@
 package middleware
 
 import (
+	"net/http"
+
 	"github.com/gin-gonic/gin"
 	"github.com/pocket-id/pocket-id/backend/internal/common"
 )
@@ -23,7 +25,7 @@ func (m *CorsMiddleware) Add() gin.HandlerFunc {
 		c.Writer.Header().Set("Access-Control-Allow-Headers", "*")
 		c.Writer.Header().Set("Access-Control-Allow-Methods", "POST, OPTIONS, GET, PUT")
 
-		if c.Request.Method == "OPTIONS" {
+		if c.Request.Method == http.MethodOptions {
 			c.AbortWithStatus(204)
 			return
 		}