We're removing support for Import of agent tokens in the Terraform provider. This change coincides with the announcement in this changelog. From 4 July 2023 onwards, any resources or data-sources which are dependent on an agent token being present will likely fail to apply.
We recommend that you update your provider version to >=0.19.0. Any version below this will run a state refresh on the next Terraform operation and cause agent tokens in state to be set to nil, "". If these changes are then deployed, there is a risk that all agents in your organisation will have their tokens removed and no longer be able to connect to Buildkite.