Or-or you could do it the really long and harder method of using the Data Editor instead of short-cutting it through triggers. It'll be really hard but you'll be thankful for learning this later. You ready? Its the data editor so it'll be really long and tedious compared to triggers editor to get the job done, here it is:
Go to Unit Flags, uncheck the one that says turnable, and if Turn before moving one is checked, uncheck that one too.
Oh wow that was a lot, but hey, it gets the job done at least.