Hope this is the correct way to deal with this kind of issue (a quick search on meta-stackexchange seems to confirm this).
I would suggest to add a tag synonym for [my-site] -> [my-sites] (but don't have the rep to). Seems there are multiple questions that uses both tag, and I can't see a real difference between the two.
Anyone can open the synonym request? Or should we delete the [my-sites] tag (only 22 question, we should be able to switch the tags manually if we have to)??