dev/ci: build sg as dev build in CI, improve lib/output error message
Created by: bobheadxi
Because we set the version, auto update defaults to true, which means we get sg attempting to update itself in CI
https://buildkite.com/sourcegraph/sourcegraph/builds/150797#01811aa2-5403-48ab-aac3-a12c29bc511f
Test plan
yolo let's test in main