[BUG] Crash on garbage collection with python 3.9

I'm wrapping the python logger on c++ side and for convenience store the logger attributes "debug", "info", "warning" and "error" in some class members. The logger is initialized by name via the getLogger function in python and is then kept as a global variable. This works fine with python <= 3.8, but causes an issue during garbage collection in python 3.9, resulting in a non-zero exit code.

Please consider the following reproducer.

In c++ with pybind 2.4.2 (also tried 2.6.2):

#include <pybind11/pybind11.h>

namespace py = pybind11;

namespace {
    struct NamedLogger 
    {
        const std::string name;
        py::object logger;
        py::object debug;
        py::object info;
        py::object warning;
        py::object error;

        NamedLogger(const std::string& name_)
            : name(name_) 
        {
            auto logging = py::module::import("logging");
            auto getLogger = logging.attr("getLogger");
            logger = getLogger(name);

            debug = logger.attr("debug");
            info = logger.attr("info");
            warning = logger.attr("warning");
            error = logger.attr("error");
        }
    };

    std::unique_ptr<NamedLogger> logger;

} // namespace

// Module ======================================================================
PYBIND11_MODULE( logger_cpp, mod ) 
{
    logger.reset( new NamedLogger("MyLogger") );
    logger->debug( "I'm alive" );
}

Then simply run

python -c "import logger_cpp"

Start with the PYBIND11_MODULE reproducer and run python -c "import logger_cpp" under Python 3.9, comparing it with Python 3.8. Trace the global NamedLogger and its stored logger attributes during interpreter garbage collection; done means the import exits cleanly with code 0 on Python 3.9.