Villagers don't get scared of giants, and won't spawn an iron golem in defence.
How to reproduce:
Get some villagers (at least three, by spawneggs, commands or in the wild)
Summon a Giant with the command: /summon minecraft:giant ~ ~ ~ {Invulnerable:true} (this step of course near the villagers.
Note that the villagers will still refresh their trades and won't run away.
Since snapshot 19w03a, Giants' AI was reverted back and villagers don't run away nor get infected by giants. So this hasn't been a bug since.