by Leon Stringer.
If you're familiar with working with MariaDB at the shell or using phpMyAdmin you could try running that query manually and seeing if it works, e.g.:
INSERT INTO mdl_task_log (type, component, classname, userid, timestart,
timeend, dbreads, dbwrites, result, output)
VALUES (0, 'logstore_standard', 'logstore_standard\\task\\cleanup_task', 0,
1563856022.3714321, 1563856022.4131601, 2, 999, 0,
'Execute scheduled task: Čiščenje tabele dnevnikov (logstore_standard\\task\\cleanup_task)
Deleted old log records from standard store.
... used 3 dbqueries
... used 0,042447090148926 seconds
Scheduled task complete: Čiščenje tabele dnevnikov (logstore_standard\\task\\cleanup_task)');
I've set dbwrites to 999 so you can hopefully identify the row to remove it. Take a database backup before making any changes to be safe.
The values on the second "Column count doesn't match..." error look correct, i.e. the 10th value (index 9 in the array) has the terminating single quote as expected, the extra comma after is because Moodle is using var_export() to show the array, i.e. it's expected.
Let us know If the above INSERT works or not, and any error you see. Also the output of SHOW CREATE TABLE mdl_task_log would let us check the table definition.