Need to redeclare default registry with scopes

[Electroid]

Took a longggg time to get this working with multiple registries (GitHub private, and npm public), but eventually got there.

Because GitHub doesn't forward a MISS to npm

If adding a scoped registry, you have to redeclare the default registry!

[install]
registry = "https://registry.npmjs.org" # redeclare default!

[install.scopes]
"@acme" = { token = "$ACME_TOKEN", url = "https://npm.pkg.github.com/" }
#                     ^ loads from .env file(s)
# add any other scoped registries (with their own access tokens)

Originally posted by @lukeed in #4654 (comment)

[lukeed]

Relatedly, install should allow multiple registries to be configured. That's a core part of .npmrc (esp root level)

[Jarred-Sumner]

@dylan-conway does this still occur? Do we have any tests that check this?