Several minor bugs in `test_typing` highlighted by pyflakes

[AlexWaygood]

Following #102437 by @JosephSBoyle, I tried running pyflakes on test_typing.py. It highlighted:

• Another instance where a test isn't testing what it was meant to be testing
• An instance where a test is entirely duplicated
• Several unused imports or variables.

Linked PRs

• gh-102444: Fix minor bugs in test_typing highlighted by pyflakes #102445
• [3.11] gh-102444: Fix minor bugs in test_typing highlighted by pyflakes (GH-102445) #102451
• [3.10] gh-102444: Fix minor bugs in test_typing highlighted by pyflakes (#102445) #102452