Wall of Stolen Identity's ability shouldn't let the creature it copies untap

The title says it all: the creature that Wall of Stolen Identity ETBs as shouldn't untap during its controller's untap step, as long as you control Wall of Stolen Identity.

No source file or test is named in the issue. Locate the implementation and tests for Wall of Stolen Identity, then verify the copied creature's untap behavior while its controller still controls the Wall; done means the behavior matches the card text.

Written by the indexing model from the issue text.