SWC download fails because of a missing trailing slash in the custom registry

[ghostd]

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #1 SMP Wed Mar 2 18:50:46 UTC 2022
Binaries:
  Node: 14.18.2
  npm: 6.14.15
  Yarn: 1.22.15
  pnpm: N/A
Relevant packages:
  next: 12.2.4
  eslint-config-next: N/A
  react: 17.0.2
  react-dom: 17.0.2

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

While building the production site (with "next build") on our CI, I get this error:

info  - Creating an optimized production build...
info  - Downloading WASM swc package...
warn  - Attempted to load @next/swc-linux-x64-gnu, but it was not installed
warn  - Attempted to load @next/swc-linux-x64-gnux32, but it was not installed
warn  - Attempted to load @next/swc-linux-x64-musl, but it was not installed
warn  - Error: request failed with status 404
    at /builds/xxx/node_modules/next/dist/lib/download-wasm-swc.js:124:23
    at processTicksAndRejections (internal/process/task_queues.js:95:5)
    at async Object.downloadWasmSwc (/builds/xxx/node_modules/next/dist/lib/download-wasm-swc.js:122:9)
    at async /builds/xxx/node_modules/next/dist/build/swc/index.js:114:13
error - Failed to load SWC binary for linux/x64, see more info here: https://nextjs.org/docs/messages/failed-loading-swc

After digging, I found npm config get registry can return a value without a trailing slash, something like : http://artifactory.private.domain/artifactory/api/npm/all-npm

And the download code assumes a trailing slash:

next.js/packages/next/lib/download-wasm-swc.ts

Lines 81 to 90 in 5d93753

	let registry = `https://registry.npmjs.org/`
	try {
	const output = execSync('npm config get registry').toString().trim()
	if (output.startsWith('http')) {
	registry = output
	}
	} catch (_) {}
	await fetch(`${registry}${pkgName}/-/${tarFileName}`).then((res) => {

Expected Behavior

Since I cannot change the npm settings on my CI, i wonder if the NextJs script can be more resilient by checking the result of the command npm config get registry: if the string does not end with a /, it adds it before calling fetch

Link to reproduction

none

To Reproduce

Have npm settings with a custom URL registry without the trailing slash.
Build the production bundle.

[github-actions]

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