[exceptions] fix string conversion for Unauthorized exception changeset 3cb87b61b067 changed CubicWebException to define __unicode__ as the main entry point for string conversion, but left Unauthorized's __str__ definition unchanged, leading to a mismatch. Closes #10646396.

for table, column in [
        ('transactions', 'tx_time'),
        ('tx_entity_actions', 'tx_uuid'),
        ('tx_relation_actions', 'tx_uuid')]:
    repo.system_source.create_index(session, table, column)

commit()