dev/ci: disable yarn cache for now
Created by: bobheadxi
https://app.incident.io/incidents/101
Test plan
main-dry-run: https://buildkite.com/sourcegraph/sourcegraph/builds/146612
Created by: bobheadxi
https://app.incident.io/incidents/101
main-dry-run: https://buildkite.com/sourcegraph/sourcegraph/builds/146612