Zoglins, hoglins, and ravagers all do a little knockback when they hit a player holding a shield. However, iron golems don't give players knockback when they hold a shield even when they can fling players without a shield. Zoglins and Hoglins can fling players just like iron golems except that they can knock players upwards even when holding a shield. Iron golems should also have the same behavior as zoglins, hoglins, and ravagers.
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Can confirm in 21w08b.

Can confirm in 21w08b

yes, because they don't have the attack knockback attribute which was added way after golems were introduced, unlike the other mobs you mentioned.
Seems like i was wrong here, that attribute doesn't work on iron golems, and doesn't work on shields either as per MC-235198.

In 1.18 Pre-1

In 22w05a
Can confirm