Add flake8 B905 to extend-ignore in setup.cfg

[rwgk]

Description

I believe (but I'm not actually sure) that the recent flake8 dependabot upgrade from 5.0.4 to 6.0.0, combined with github switching ubuntu-latest from 20.04 to 22.04, is leading to these pre-commit failures:

flake8...................................................................Failed
- hook id: flake8
- exit code: 1

tests/test_smart_ptr.py:49:17: B905 `zip()` without an explicit `strict=` parameter.
    for i, o in zip(
                ^
tests/test_smart_ptr.py:72:17: B905 `zip()` without an explicit `strict=` parameter.
    for i, o in zip(
                ^
tests/test_stl_binders.py:192:17: B905 `zip()` without an explicit `strict=` parameter.
    assert list(zip(um.keys(), um.values())) == list(um.items())
                ^

This is one of the "Opinionated warnings" and for Python >= 3.10 only:

• https://github.com/PyCQA/flake8-bugbear#opinionated-warnings

The strict= argument was added in Python 3.10, so don't enable this flag for code that should work on < 3.10.

I.e. we cannot enable it until we drop 3.9 (https://endoflife.date/python for 3.9 is October 2025).

Suggested changelog entry:

[rwgk]

I canceled the CI workflow to not burn so many cycles for a no-op.

[rwgk]

Thanks Aaron!