Link to the code that reproduces this issue

https://github.com/AkifumiSato/pages-to-app-router-demo

To Reproduce

1. implement getServerSideProps with fetch.
2. next dev --experimental-test-proxy
3. page access with playwright test.

Current vs. Expected behavior

The following error occurs.

> playwright test
[WebServer]  ⨯ Error: No test info for GET https://dummyjson.com/products/1
    at handleFetch (/Users/xxxx/work/git/sandbox/pages-to-app-router-demo/node_modules/.pnpm/next@14.1.0_@babel+core@7.23.9_react-dom@18.2.0_react@18.2.0/node_modules/next/dist/experimental/testmode/fetch.js:89:15)
...

I would like to see a statement in the documentation that it does not work with Pages Router.
Ideally, msw would work with Pages Router as well.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 21.6.0: Wed Oct  4 23:56:02 PDT 2023; root:xnu-8020.240.18.704.15~1/RELEASE_ARM64_T6000
Binaries:
  Node: 18.17.0
  npm: 9.8.0
  Yarn: N/A
  pnpm: 8.9.0
Relevant Packages:
  next: 14.1.0
  eslint-config-next: 14.1.0
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.3.3
Next.js Config:
  output: N/A

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

Data fetching (gS(S)P, getInitialProps)

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

next dev (local), next start (local), Other (Deployed)

Additional context

No response