tl,dr; Update agents to 2.2.0b8 or later before updating the site to 2.3.0!
With this Werk Checkmk will no longer generate and validate SHA1 signatures for agent packages.
With Werk #15692 Checkmk generated SHA256 signatures and the agent-updater is capable to verify SHA256 signatures since 2.2.0b8.
If you have agent updaters older than 2.2.0b8 these will not be able to verify agent packages anymore and therefore need manual updating after this Werk.
We recommend to install at least 2.2.0p8 and update all agents before updating to 2.3.0.
If you were on 2.2.0p8 or beyond and all agents are up-to-date then no intervention will be necessary.
To the list of all Werks