Use %zd printf format in the C code of Python

[vstinner]

Python 3.12 now requires a C11 compiler. We don't have to check if the %zd printf format is supported: it's available since C99. Python 3.6 requires a C99 compiler to build.

The PY_FORMAT_SIZE_T macro was already updated to be always defined as "z": commit d765d81.

This issue is a follow-up of the previous issue #81962.

[vstinner]

Fixed by #93201