🧹 chore: harden cache post test counter

Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/c0423e5f-7f46-4ba0-ba0b-ef41c6eb7933

Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Author: Copilot

middleware/cache/cache_test.go

@@ -936,10 +936,10 @@ func Test_Cache_Post(t *testing.T) {
 
 	app.Use(New())
 
-	count := 0
+	var count atomic.Int32
 	app.Post("/", func(c fiber.Ctx) error {
-		count++
-		return c.SendString(fmt.Sprintf("%d:%s", count, fiber.Query[string](c, "cache")))
+		current := count.Add(1)
+		return c.SendString(fmt.Sprintf("%d:%s", current, fiber.Query[string](c, "cache")))
 	})
 
 	resp, err := app.Test(httptest.NewRequest(fiber.MethodPost, "/?cache=123", http.NoBody))