[3.12] gh-119577: Adjust DeprecationWarning when testing element truth values in Element tree (GH-119762) (#120190)

gh-119577: Adjust DeprecationWarning when testing element truth values in ElementTree (GH-119762)

Adjust DeprecationWarning when testing element truth values in
ElementTree, we're planning to go with the more natural True return
rather than a disruptive harder to code around exception raise, and are
deferring the behavior change for a few more releases.

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>