Fix "truthy"/"falsy" in documentation #161077

Documentation

See my retracted PR #158663. The previous times I created issues (#89509 and #95454) and they got fixed right away, it seems creating a PR was a mistake, so I'm filling this issue instead.

(It's a pity especially right now, since one of the "truthy" is in the documentation of sentinel, a prominent Python 3.15 feature. It might be spreading into news/tutorials and learners' minds from there, I was hoping to prevent that by fixing this before the release.)