Steps to reproduce:

1. Update was performed according to the instructions https://www.zabbix.com/documentation/4.4/manual/installation/upgrade/packages/debian_ubuntu
2. Final stage upgrade database is failed, error 5603:20191022:170247.150 [Z3005] query failed: [1366] Incorrect string value: '\xD0\x9C\xD0\xB0\xD0\xB9...' for column 'os' at row 2 [insert into host_inventory (select * from host_inventory_tmp)]
3. I opened phpMyAdmin and run SQL query SELECT * FROM `host_inventory_tmp` WHERE `os` LIKE "%Майкрософт%"
4. I changed the values from "Майкрософт" to "Microsoft" for all search rows
5. Upgrade was successful

Result:
See log file.