bpo-40915: Fix a 32bit compiler warning in mmapmodule.c on Windows

[neonene]

MSVC(x86) shows the following warning at mmap_resize_method() when building 3.11.

mmapmodule.c(539,58): warning C4244: '=':
conversion from 'LONGLONG' to 'Py_ssize_t', possible loss of data

https://bugs.python.org/issue40915

[miss-islington]

Thanks @neonene for the PR, and @zooba for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

[miss-islington]

Sorry, @neonene and @zooba, I could not cleanly backport this to 3.10 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 6214caafbe66e34e84c1809abf0b7aab6791956b 3.10

[miss-islington]

Sorry @neonene and @zooba, I had trouble checking out the 3.9 backport branch.
Please backport using cherry_picker on command line.
cherry_picker 6214caafbe66e34e84c1809abf0b7aab6791956b 3.9

[zooba]

I don't have time right now to do backports, so if someone else wants to go right ahead. Remember to put [3.10] and [3.9] in the title of the PR

[neonene]

Only 3.11 changed mmapmodule.c and emits the warning.

[neonene]

Thanks @zooba and @AlexWaygood for the help.