multi set-cookie merged into one header when cookie name is same

### Link to the code that reproduces this issue https://github.com/yeliex/stackblitz-starters-kfmrzz ### To Reproduce ``` yarn yarn dev ``` then open `${host}/api/test`, open dev-tools or read terminal output, you would find `set-cookie` headers. ### Current vs. Expected behavior ### Expected ``` set-cookie: session=1713406956812; Path=/; Domain=.example1.com; Secure; HttpOnly; SameSite=none set-cookie: session=1713406956812; Path=/; Domain=.example2.com; Secure; HttpOnly; SameSite=none ``` ### Current ``` ## server response set-cookie: session=1713406956812; Path=/; Domain=.example1.com; Secure; HttpOnly; SameSite=none, session=1713406956812; Path=/; Domain=.example2.com; Secure; HttpOnly; SameSite=none ## dev-tools response header Set-Cookie: session=1713407480483; Path=/; Domain=.example2.com; Secure; HttpOnly; SameSite=none ``` ### Provide environment information ```bash Operating System: Platform: linux Arch: x64 Version: #1 SMP PREEMPT_DYNAMIC Sun Aug 6 20:05:33 UTC 2023 Available memory (MB): 4102 Available CPU cores: 2 Binaries: Node: 20.12.0 npm: 10.5.0 Yarn: 1.22.19 pnpm: 8.15.6 Relevant Packages: next: 14.3.0-canary.9 // Latest available version is detected (14.3.0-canary.9). eslint-config-next: N/A react: 18.2.0 react-dom: 18.2.0 typescript: 5.2.2 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Not sure ### Which stage(s) are affected? (Select all that apply) next dev (local), Other (Deployed) ### Additional context when set multi cookie with same name, it would merged into one `set-cookie` header, then when response to client, only the last one remains