R1:968ac764532d

Don't adjust task priority after a workboard drag unless we need to

Summary:
Fixes T8197. Currently, if you priority-sort a workboard and drag a card to the top or bottom, we change the priority even if we do not need to.

For example, if the lowest priority in a column is "Low", and you drag a "Wishlist" task underneath it, we incorrectly increase the priority of the task to "Low", when we do not actually need to touch it. This is bad/confusing.

A similar thing happens when dragging a "High" priority…