Canonical URLs with path extension (e.g. .html) get a trailing slash when it shouldn't

[kshehadeh]

Link to the code that reproduces this issue

kshehadeh/nextjs-routing-sandbox@04fffc1

To Reproduce

1. Set the trailingSlash config for a project to true
2. Add an app router page that includes a generateMetadata which returns a canonical url that ends with .html
3. Run page and observe that canonical ends with .html/

Current vs. Expected behavior

Current: canonical ends with .html/
Expected: canonical ends with .html

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.5.0: Wed May  1 20:14:38 PDT 2024; root:xnu-10063.121.3~5/RELEASE_ARM64_T6020
  Available memory (MB): 16384
  Available CPU cores: 12
Binaries:
  Node: 18.17.0
  npm: 10.2.5
  Yarn: N/A
  pnpm: 8.15.7
Relevant Packages:
  next: 14.2.3 // Latest available version is detected (14.2.3).
  eslint-config-next: 14.0.0
  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)

Metadata

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

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

Additional context

I believe it was introduced with this PR: https://github.com/vercel/next.js/pull/62109/files

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