[BUG]: py::py::mod_gil_not_used() maybe not support python 3.14.0 free threaded feature, when using callback function

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What version (or hash if on master) of pybind11 are you using?

3.0.1

Problem description

c++ wrapper.cc

PYBIND11_MODULE(demo, m, py::mod_gil_not_used()) {
m.def(
"callback",
[](py::function cb) {
cb("aaa");
cb("bbb");

        std::future<void> f1 = std::async(std::launch::async, [cb] {
            cb("aaa");
        });
        std::future<void> f2 = std::async(std::launch::async, [cb] {
            cb("bbb");
        });
        f1.get();
        f2.get();
    },
    "Call a Python callback from C++");

}

demo.py:

def fun(a):
print("Hello", a)
import time
time.sleep(3)
print("Hello-----", a)

kcal.callback(fun)

When I run this function, the program raise "Segmentation fault (core dumped)"

Reproducible example code

Is this a regression? Put the last known working version here if it is.

Not a regression

Start by building the wrapper.cc example with py::mod_gil_not_used() and running demo.py under Python 3.14.0's free-threaded mode. Inspect the callback entry point and its two std::async calls, then reproduce the segmentation fault with the provided Python callback. Done means concurrent callbacks complete without a crash.