[3.13] gh-129350: Make tests for glob with trailing slash more strict (GH-129376) (GH-129651)

Test that the trailing pathname separator is preserved.

Multiple trailing pathname separators are only preserved if the pattern
does not contain metacharacters, otherwise only one trailing pathname
separator is preserved. This is rather an implementation detail.
(cherry picked from commit 8b5c8508c7f5d98b09792e159ef2396c73da68cd)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>