Those are Dropbox notifications, not ones from KM, so you need to adjust your Dropbox settings. I also highly suggest you turn KM's notifications back on, since they only provide useful info like error messages or notifications from macros that you choose to include with the "Display Text Briefly" or "Notification" actions.
Doh! If I'd paid more attention to the icon on the notification, I would have figured that out. The file being changed is an AppleScript that happens to sit in a folder called "Keyboard Maestro" on Dropbox, hence the label on the notification.