Py_buffer::format is implemented as `char*` instead of `const char*`

[maxbachmann]

Bug report

The format member in Py_buffer is documented to have the type const char*. However the actual type is char*:

cpython/Include/pybuffer.h

Line 28 in ec091bd

char *format;

[cmaloney]

This is fixed for Python 3.12+ by gh-119467; Another contributor came across the same issue and contributed a patch.