Argument of type ShadowRoot | null is not assignable to parameter of type Element | undefined .

`qunit-dom` does work correctly with `ShadowRoot`, but its types do not allow for that.

Reproduction:  https://github.com/lifeart/glimmer-next/blob/fa5b80ac09fe52c5b6660946cc44fa103aaba627/src/tests/integration/shadowroot-test.gts#L17C1-L18

CC @lifeart