bump marshal version to 5

[nschloe]

Fixes #5568.

[bschoenmaeckers]

What happens when this new version is used on a python before 3.14?

[nschloe]

There's no change in behavior for any other Python version; see https://github.com/python/cpython/blob/main/Python/marshal.c. In principle we could set the version to 99. Not sure if this is an implementation detail or a feature though.

Edit: I asked for clarification here.