[3.12] GH-106160: Fix test_gzip failing under WASI, which does not have zlib. (GH-106167) (#106170)

GH-106160: Fix test_gzip failing under WASI, which does not have zlib. (GH-106167)

Fix test_gzip's failure under WASI, which does not have zlib, by using
test.support.import_helper.import_module to import zlib. (gzip
unconditionally imports zlib, so this does not cause any new skips.)
(cherry picked from commit 161012fc25910a47423bae8012398bf519a88140)

Co-authored-by: T. Wouters <thomas@python.org>