bpo-44955: Always call stopTestRun() for implicitly created TestResult objects (GH-27831)

Method stopTestRun() is now always called in pair with method startTestRun()
for TestResult objects implicitly created in TestCase.run().
Previously it was not called for test methods and classes decorated with
a skipping decorator.
(cherry picked from commit a9640d75531d6cbbfd254b65435f238c26bf5cd9)

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