🐛 Default error handler for mounted app

[lucaskatayama]

Fiber version
v2.22.0
Issue description

If you mount an router in a group, the default error handler is not triggered.

Code snippet

Given router:

**Router **

func Router() *fiber.App {
	api := fiber.New(fiber.Config{
		ErrorHandler: ErrorHandler,
	})

	for _, route := range Routes {
		api.Add(route.Method, route.Path, route.Handler)
	}
	return api
}

The following code does not trigger the default error handler inside v1.Router() or v2.Router()

Main

package main

import "github.com/gofiber/fiber/v2"

func main() {
  app := fiber.New()
  api := app.Group("/api")
  api.Mount("/v1", v1.Router())
  api.Mount("/v2", v2.Router())
}

BUT if you do the following it works:

Main

package main

import "github.com/gofiber/fiber/v2"

func main() {
  app := fiber.New()
  app.Mount("/api/v1", v1.Router())
  app.Mount("/api/v2", v2.Router())
}

And the specific router error handler is called correctly.

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