[3.11] gh-111803: Make test_deep_nesting from test_plistlib more strict (GH-114026) (GH-114407)

It is no longer silently passed if RecursionError was raised for low
recursion depth.
(cherry picked from commit db1c18eb6220653290a3ba9ebbe1df44394a3f19)

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