Fix GH-98360, Fix similar triangles exercise not accepting correct answers

Here is a bug fix for GH-98360.

Similar triangles was not accepting correct answers in the case where `data-ensure` looped more than once. This affected problem types `height-b` and `side-b`. The ensure loops were placed on the `problem div` instead of on the `vars div`. This caused the solution var to get replaced on the first loop and therefore would not be updated on subsequent data-ensure loops.