[3.14] gh-89152: Note truth testing exception in `stdtypes.rst` (GH-137640) (#143081)

gh-89152: Note truth testing exception in `stdtypes.rst` (GH-137640)
(cherry picked from commit 3c0888b25b4c1dc1dee6d0edf05d51d3cc24486e)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>