MariaDB compatibility fix

Summary: Unlike MySQL it includes microseconds in the datetime output.

Reviewers: Syncroton Developers, mollekopf

Reviewed By: Syncroton Developers, mollekopf

Subscribers: mollekopf, Syncroton Developers

Differential Revision: https://git.kolab.org/D4860

This is supposed to address duplicates entry errors like this:

18-Jul-2024 06:06:18.022995]: DB Error: [1062] Duplicate entry 'b01e521ea8f3d9ca60f6d1d908741e77947c2d6f-da698d43c260bdb9dd6a...'
for key 'PRIMARY' (SQL Query: INSERT INTO syncroton_relations_state (device_id, folder_id, synctime, data) VALUES ('b01e5
21ea8f3d9ca60f6d1d908741e77947c2d6f', 'da698d43c260bdb9dd6a52a9a44786fb', '2024-07-18 06:06:18', ...