[3.10] gh-77607: Improve accuracy of os.path.join docs (GH-101406) #101452
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This is a follow-up to GH-100811.
One of the changes in that PR isn't accurate in that
os.path.join('', '')will not end in a separator.This reverts that change to the previous wording that used "only", but
explicitly calls out the case where the last part ends in a separator,
which is what caused confusin in GH-77607 and motivated the change
in GH-100811.
(cherry picked from commit 909a674)
Co-authored-by: Shantanu 12621235+hauntsaninja@users.noreply.github.com