Timeout behavior regression in v1.2.1

Summary

There appears to be a regression in github.com/gin-contrib/timeout starting from v1.2.1.
The timeout middleware does not terminate the request at the configured timeout duration and instead waits until the handler completes.

Environment

• github.com/gin-contrib/timeout: v1.2.1
• github.com/gin-gonic/gin: v1.12.0

Reproduction

1. Use the following test code

package main

import (
	"log"
	"net/http"
	"time"

	"github.com/gin-contrib/timeout"
	"github.com/gin-gonic/gin"
)

func testResponse(c *gin.Context) {
	c.String(http.StatusRequestTimeout, "timeout")
}

func timeoutMiddleware() gin.HandlerFunc {
	return timeout.New(
		timeout.WithTimeout(time.Second),
		timeout.WithResponse(testResponse),
	)
}

func main() {
	r := gin.New()
	r.Use(timeoutMiddleware())
	r.GET("/slow", func(c *gin.Context) {
		time.Sleep(5 * time.Second)
		c.Status(http.StatusOK)
	})
	if err := r.Run(":8080"); err != nil {
		log.Fatal(err)
	}
}

2. Run the server

$ go run main.go

3. Call the endpoint

$ curl http://localhost:8080/slow -w "%{time_total} sec\n"

Results

Using gin-contrib/timeout v1.2.1:

5.001918 sec

Using gin-contrib/timeout v1.2.0:

1.001925 sec

Expected Behavior

When a timeout of 1 second is configured, the request should be terminated after ~1 second, and the timeout response should be returned.

Actual Behavior

• With v1.2.1, the request completes after ~5 seconds (the handler duration), not respecting the timeout.
• With v1.2.0, the timeout works correctly and returns after ~1 second.

Start with the timeout middleware behavior in github.com/gin-contrib/timeout v1.2.1 and compare it with v1.2.0. Run the provided Go reproduction with Gin v1.12.0; done means the /slow request returns the timeout response after about one second instead of waiting five seconds.