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Crash when loading 'registry' package from NPM

https://sentry.softwareheritage.org/organizations/swh/issues/10902/?referrer=phabricator_plugin

KeyError: 'versions'
  File "swh/loader/package/loader.py", line 575, in load
    versions = self.get_versions()
  File "swh/loader/package/npm/loader.py", line 127, in get_versions
    return sorted(list(self.info()["versions"].keys()))

This is because we load package information from the URL https://replicate.npmjs.com/$PACKAGE_NAME, but https://replicate.npmjs.com/registry/ returns completely different data: it's metadata about the package registry itself, instead of the package named registry.

Migrated from T4443 (view on Phabricator)