Public devops npm feeds should not require auth

When consuming typespec-python emitter alpha packages in azure-sdk-for-python, the devops feed is returning 401 responses and npm install is failing.

This shouldn't require authentication. The full auth behavior needs to be tested for public feeds with upstream enabled.

The payload names no implementation file or test. Start by locating the code that handles npm authentication for public feeds with upstream enabled, then reproduce the 401 while consuming the typespec-python emitter alpha packages; done means the feed is installable without auth and the full authentication behavior is covered by tests.

Written by the indexing model from the issue text.