fix matching of missing-github-token error
Created by: sqs
The error returned by the server is must provide github_token
(see https://sourcegraph.com/github.com/sourcegraph/sourcegraph@c46dd67b4682266cae719ac380f5a4ca694509db/-/blob/enterprise/internal/codeintel/lsifserver/proxy/auth.go#L45:47).