bpo-28617 Fixed docs inaccuracies about the types that support membership tests (GH-9086)


<!-- issue-number: [bpo-28617](https://www.bugs.python.org/issue28617) -->
https://bugs.python.org/issue28617
<!-- /issue-number -->
(cherry picked from commit 08bcf647d8a92e4bd47531588b284c6820b7a7ef)

Co-authored-by: wim glenn <wim.glenn@gmail.com>
2 files changed