Update Forms test with SC interpretation

[kengdoj]

From #486 (comment):

I think there is some opportunity to add clarification in the baseline to avoid confusion and explain our interpretation for users, especially given that folks may combine these in one test process for alignment. Under 3.3.2, I think we should extract the following text from the Understanding and place it directly in the baseline to strengthen why we interpreted 3.3.2 in this specific way: "While this Success Criterion requires that controls and inputs have labels or instructions, whether or not labels (if used) are sufficiently clear or descriptive is covered separately by 2.4.6: Headings and Labels."