MacBookPro with Mojave 10.14.3 turns wi-fi on by itself when in sleep mode

My MacBookPro 13" (mid-2014) turns its wi-fi on all by itself when in sleep mode overnight.

Some years ago, Apple engineers were supposed to have solved this problem, but it has obviously recurred with Mojave 10.14.3. Does anyone have a fix for this? Obviously I could simply shut it down overnight, but it seems more convenient to leave it in sleep mode then.