bpo-34596: Fallback to a default reason when @unittest.skip is uncalled (GH-9082) (#15781)

* bpo-34596: Fallback to a default reason when @unittest.skip is uncalled

* Change default reason to empty string

* Fix rst formatting of NEWS entry
(cherry picked from commit d5fd75c53fad7049fc640c9a6162d35f0c5bea03)

Co-authored-by: Naitree Zhu <Naitreey@gmail.com>
3 files changed