Log Message:
py-contourpy: reflect correct minimum py-pybind11 dependency

Separate from what upstream documents in their issue #451, some older
versions of py-pybind11 accepted previously here would result in a
build failure like so:

../src/wrap.cpp:21:54: error: macro "PYBIND11_MODULE" passed 3 \ 
arguments, but takes just 2
 PYBIND11_MODULE(_contourpy, m, py::mod_gil_not_used()) {
                                                      ^
../src/wrap.cpp:21:1: error: 'PYBIND11_MODULE' does not name a type
 PYBIND11_MODULE(_contourpy, m, py::mod_gil_not_used()) {
 ^~~~~~~~~~~~~~~