[3.12] gh-112795: Allow `/` folder in a zipfile (GH-112932) (#113789)

gh-112795: Allow `/` folder in a zipfile (GH-112932)

Allow extraction (no-op) of a "/" folder in a zipfile, they are commonly added by some archive creation tools.

(cherry picked from commit 541c5dbb81c784afd587406be2cc82645979a107)

Co-authored-by: AN Long <aisk@users.noreply.github.com>
Co-authored-by: Erlend E. Aasland <erlend@python.org>
Co-authored-by: Gregory P. Smith <greg@krypto.org>