Triggered GainControlTargetEffect not discarding when failing due to Guardian Beast

[Cguy7777]

Tested on latest commit ff4bd9b.

To reproduce:

1. Your opponent controls an untapped [[Guardian Beast]] and a noncreature artifact.
2. Cast [[Zealous Conscripts]], target your opponent's artifact with its ETB, and let that resolve.
3. Any time later during that turn, tap or destroy Guardian Beast.

Expected result:
You never gain control of the artifact at any point.

Actual result:
When Guardian Beast leaves the battlefield or becomes tapped, you immediately gain control of the artifact.

I believe this is related to this instanceof check in GainControlTargetEffect.

[github-actions]

Guardian Beast - (Gatherer) (Scryfall) (EDHREC)

{3}{B}
Creature — Beast
2/4
As long as Guardian Beast is untapped, noncreature artifacts you control can't be enchanted, they have indestructible, and other players can't gain control of them. This effect doesn't remove Auras already attached to those artifacts.

Zealous Conscripts - (Gatherer) (Scryfall) (EDHREC)

{4}{R}
Creature — Human Warrior
3/3
Haste
When Zealous Conscripts enters the battlefield, gain control of target permanent until end of turn. Untap that permanent. It gains haste until end of turn.