checkbox does not count as update

[Klar]

In a card the checkbox does not count as an update.

Not changing the "last updated" when creating a new checkbox, editing text, check / uncheck it.

I think this is needed as otherwise the "auto close" will move the card even when there was a checkbox update.

[flavorjones]

A pull request to update last_active_at when a task is checked off would be welcome!