[3.14] gh-140578: Doc: Remove sencence implying that concurrent.futures.ThreadPoolExecutor does not exist (GH-140689) (#141382)

gh-140578: Doc: Remove sencence implying that concurrent.futures.ThreadPoolExecutor does not exist (GH-140689)

* Doc: Remove sencence implying that concurrent.futures.ThreadPoolExecutor does not exist

Closes GH-140578

* Add NEWS.d entry for gh-140578

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(cherry picked from commit 46b58e1bb9e1e17d855588935f5a259be960a3a1)

Co-authored-by: Louis <paternal@users.noreply.github.com>
Co-authored-by: Louis Paternault <spalax@gresille.org>