* fix Unsettled Mariner + Field of Ruin
There was something weird with zcc on TargetOfOpponentsSpellOrAbilityTriggeredAbility
setting the target to the stack object for its triggered effect.
I do not entirely comprehend how FixedTarget works, in particular regarding zcc of stack objects.
However all configurations of the trigger seem to work with the uninitialized FixedTarget constructor,
instead of the one initialized with a game's zcc.
* slight refactor of TargetOfOpponentsSpellOrAbilityTriggeredAbility
