I haven't actually. I think I'm going to wait and see first. Sky will write to me in the next few days if there are any charges. As JohnH1 pointed out earlier, I've already paid up front for the final month so it'd be a bit harsh if they charged me early termination fees on top of that.
Also on https://www.sky.com/help/articles/charges-for-ending-your-sky-contract-early it says the following. I've bolded the bit I think is relevant.
The amount you're charged depends on:
OK, so I heard back from Sky by letter. I won't incur any early termination charges for this transfer.
I guess as I'm already fully paid-up for the final month there are no charges, which is good news and makes it easier.