Bumps alpine from 3.8 to 3.9.2. (#408)
By side-effect, bumps syslog-ng from 3.13.2-r3 to 3.19.1-r0, which causes warning messages to appear:
[timestamp] WARNING: Configuration file format is too old, syslog-ng is running in compatibility mode. Please update it to use the syslog-ng 3.19 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.;
[timestamp] WARNING: With use-dns(no), dns-cache() will be forced to 'no' too!;
This is fixed in #423