In the testing guide, add red note at end to say it's real or test data

Idea from Andrew

This is a convenient double check for data collectors. The very last question in a form can ask them to confirm whether they are collecting real data or not.

Locate the testing guide in the documentation repository and read its final question or form-related section. Add the requested red note at the end, making clear whether the collected data is real or test data; the work is done when the guide visibly includes this final confirmation question.

Written by the indexing model from the issue text.