[2.1.0] Checkmk Werk 14619 created: check_mailbox: update-config failed if 'ssl' key not in fetch-config

Title: check_mailbox: update-config failed if 'ssl' key not in fetch-config Class: fix Compatible: compat Component: checks Date: 1706021156 Edition: cre Level: 1 Version: 2.1.0p39 Older configurations for `check_mail` were not guaranteed to contain the `ssl` key, (de)activating TLS for connections. This change just deactivates the check for this key, keeping the functionality.