Tera Shell quarters the damage if its owner has two Types

[Nihilslave]

https://replay.pokemonshowdown.com/gen9doublesubers-2241672756-ryty01dj1vypoy3fcftnjbrdri1mzxopw
As you can see in the replay Terapagos gets an additional Grass Type by Forest's Curse. And then when Tera Shell activates it 4x resists the move instead of 2x, which shouldn't be a correct behaviour compared to real game I believe.
This is caused by Pokemon.runEffectiveness() which iters through all types of a Pokemon and for each loop it triggers onEffectiveness() of Tera Shell. And when there are more than 1 Types, Tera Shell's effect (i.e. onEffectiveness()) will be triggered more than 1 times.
I make this an issue but not a pull request because 1. I'm not sure how it really works in real game, and 2. I also don't know how to fix it in an elegant way.