Pact of the Chain Warlocks can enable their familiars to make an attack instead of them when they take the Attack action (emphasis mine):
You learn the Find Familiar spell and can cast it as a ritual. The spell doesn't count against your number of spells known. When you cast the spell, you can choose one of the normal forms for your familiar or one of the following special forms: imp, pseudodragon, quasit or sprite. Additionally, when you take the Attack action, you can forgo one of your own attacks to allow your familiar to make one attack of its own with its reaction.
And the spell Gaseous Form says that its target cannot attack (again, emphasis mine):
While in the form of a misty cloud, the target can’t talk or manipulate objects, and any objects it was carrying or holding can’t be dropped, used, or otherwise interacted with. The target can’t attack or cast spells.
So my question is can a Pact of the Chain Warlock in Gaseous Form have their familiar attack? The spell doesn't say the target can't take the attack action, but that they can't attack, and in this case the Warlock won't be doing the attacking.