Error: model already exists with URI

Created by: lguychard

I'm seeing a lot of this on Sentry (code-monitors occurences in the last 24 hours): https://sentry.io/organizations/sourcegraph/issues/986971497/?project=1334031&query=is%3Aunresolved&statsPeriod=14d

This error was added in https://github.com/sourcegraph/sourcegraph/pull/3322 cc @sqs