Cookies in `header()` are differently encoded in server action and server request.

### Link to the code that reproduces this issue https://github.com/yongholeeme/reproduction-bug-cookies-encoding-in-server-action-and-server-reqeust ### To Reproduce In production 1. Start the application in production (next build && next dev) 2. Click `redirect in server actions to /test` 3. In the third line, AAA value is encoded. ### Current vs. Expected behavior In server, there are two ways to get cookies. First, reading cookies from `cookies()` function. And another way is reading cookies in header from `headers()` function. But I found cookies in `headers()` work sort of differently between general server request and server action reqeust. In general server request, `headers().get('cookie')` returns values barely regardless of whether each value is encoded or not. However in server action request, `headers().get('cookie')` returns all values as encoded. It's totally the same code but behave differently when it's be excuted. This problem is only reproduced in production. cc <https://github.com/vercel/next.js/issues/77010> https://github.com/user-attachments/assets/c9a0f3ec-e688-4b6a-8198-9fdb072893d5 ### Provide environment information ```bash Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 24.1.0: Thu Oct 10 21:06:23 PDT 2024; root:xnu-11215.41.3~3/RELEASE_ARM64_T8132 Available memory (MB): 32768 Available CPU cores: 10 Binaries: Node: 22.11.0 npm: 10.9.0 Yarn: N/A pnpm: 9.15.4 Relevant Packages: next: 15.3.0-canary.1 // Latest available version is detected (15.3.0-canary.1). eslint-config-next: N/A react: 19.0.0 react-dom: 19.0.0 typescript: 5.8.2 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Select all that apply) Cookies, Headers, Server Actions ### Which stage(s) are affected? (Select all that apply) Vercel (Deployed), next start (local) ### Additional context _No response_