[FIX] core: An exception caused by a datetime import conflict

in master datetime (the module) is unused, so keep datetime (the class).

line 9: import datetime
line 29: from datetime import datetime, date
line 1605: datetime.datetime.strptime(mtime.split('.')[0], server_format)

type object 'datetime.datetime' has no attribute 'datetime'

closes odoo/odoo#89968

Signed-off-by: Julien Castiaux <juc@odoo.com>