main/syslog-ng: bump default config version

fixes the following warning shown on startup: [2023-02-28T17:39:31.458375] WARNING: Configuration file format is too old, syslog-ng is running in compatibility mode. Please update it to use the syslog-ng 3.38 format at your time of convenience. To upgrade the configuration, please review the warnings about incompatible changes printed by syslog-ng, and once completed change the @version header at the top of the configuration file; config-version='3.30'