Buildkite Agent v4 is here

Buildkite Agent v4 is here. It’s the first major version of the agent since v3 arrived in 2018, and it’s now the stable release: installations and upgrades that follow the latest or stable channels now receive v4. v4 clears out functionality deprecated over those eight years and makes current, supported behaviour the default, giving the agent a cleaner baseline for what we build next.