build: use lts shorthand in GitHub Actions
Rather than hard-coding GitHub Actions to use Node.js 14.x, use the
lts/* shorthand for "most recent LTS version".
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Rather than hard-coding GitHub Actions to use Node.js 14.x, use the
lts/* shorthand for "most recent LTS version".