[3.12] gh-111126: Use `isinstance` instead of `assert[Not]IsInstance` in `test_typing` (GH-111127) (#111130)

gh-111126: Use `isinstance` instead of `assert[Not]IsInstance` in `test_typing` (GH-111127)
(cherry picked from commit ea7c26e4b89c71234c4a603567a93f0a44c9cc97)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>