The AzDO schema is only applied by yaml-language-server when the file
URI matches the configured globs (azure-pipelines.yml / *.yaml). The
smoke test was using 'plain-pipeline.yml' which never matched, causing
test [8] to always return 0 completions.
Also increased didOpen → completion sleep from 0.8s to 1.5s to give
yaml-ls time to parse the 1.6MB AzDO schema JSON.