[3.13] gh-141617: clarify `concurrent.futures.ThreadPoolExecutor` deadlock example (GH-141620) (#145687)

gh-141617: clarify `concurrent.futures.ThreadPoolExecutor` deadlock example (GH-141620)

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(cherry picked from commit 171133aa84cd2fa8738bdbb0c76435645810e8d3)

Co-authored-by: Yashraj <yashrajpala8@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>