request host header is [::]:3000 in middleware when redirecting in server action

Link to the code that reproduces this issue

https://github.com/kevinmitch14/redirects

To Reproduce

1. Start application npm run build + start
2. Press submit button to trigger redirect
3. View console logs

Current vs. Expected behavior

Current: request host header is [::]:3000
Expected: request host header is localhost:3000

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.0.0: Fri Sep 15 14:41:43 PDT 2023; root:xnu-10002.1.13~1/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 20.9.0
  npm: 10.1.0
  Yarn: 1.22.19
  pnpm: 8.15.1
Relevant Packages:
  next: 14.2.0-canary.0 // Latest available version is detected (14.2.0-canary.0).
  eslint-config-next: N/A
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.1.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

App Router, Middleware / Edge (API routes, runtime)

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local)

Additional context

Host looks to be okay when deployed to Vercel. However I wasn't able to test this with subdomains.

I've tracked it down to this PR https://github.com/vercel/next.js/pull/62561. Using the canary version before this logs host as localhost:3000.

For context, our app is a multi tenant app, each tenant lives on a subdomain. We use rewrites to handle this. To get the subdomain, we use the request host header.

Reproduce the issue in the linked redirects repository by running npm run build and start, submitting the form, and inspecting the middleware console output. Compare the host behavior with the canary version before PR 62561; done means local redirects report the expected localhost:3000 host while retaining the reported tenant-host behavior.