[3.13] gh-123309: Add more tests for the pickletools module (GH-123355) (#123533)

gh-123309: Add more tests for the pickletools module (GH-123355)

Add tests for genops() and dis().
(cherry picked from commit e5a567b0a721c26c79530249d9aa159afbd11955)

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