Sync `Py_TPFLAGS_MANAGED_DICT` for PyPy3.11 across the codebase (#5537)

* Sync `Py_TPFLAGS_MANAGED_DICT` for PyPy3.11 across the codebase

Adjust the `Py_TPFLAGS_MANAGED_DICT` logic in `include/pybind11/attr.h`
to match the one used in `include/pybind11/detail/class.h`.

This is a followup to #5508.

* Use a common `#define` for pre-`Py_TPFLAGS_MANAGED_DICT` Pythons

* style: pre-commit fixes

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>