[flake8-debugger] Also flag sys.breakpointhook and sys.__breakpointhook__ (T100)

[ntBre]

Summary

Fixes #16189.

Only sys.breakpointhook is flagged by the upstream linter:
https://github.com/pylint-dev/pylint/blob/007a745c8619c2cbf59f829a8f09fc6afa6eb0f1/pylint/checkers/stdlib.py#L38

but I think it makes sense to flag __breakpointhook__ too, as suggested in the issue because it

contain[s] the original value of breakpointhook [...] in case [it happens] to get replaced with broken or alternative objects.

Test Plan

New T100 test cases

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.