Zabbix

....I..... [ZBX-22307] introduced schema-upgrade directories

Per database, these directories now host _optional_ patches for use by
the database administrator to apply at their own discretion.

Existing patches and patch generations has been moved to these
directories.

Note that double.sql has been under version control since its
introduction. For the time being, it doesn't appear that this file
/needs/ to be generated, but probably could be, but leave that to the
future me...

Not entirely sure that patch needs to be excluded from .gitignore, as
Git tracks the file, thus the do-not-ignore rule seems a bit redundant.
Keeping for now.