Python pickle `load_reduce` function doesn't check if `args` is a tuple

Bug report

Bug description:

When load_reduce() is called in Python pickle, the args variable is pulled off the stack and passed into the functions using the * operator. This syntax is type-permissive, meaning the type can be any iterable that will return the needed arguments.

https://github.com/python/cpython/blob/29acc08c8dad664cd5713cb392e5beba65724c10/Lib/pickle.py#L1723-L1727

However, in C _pickle, argtup is pulled off the stack and passed into PyObject_CallObject(), which checks if the args parameter is specifically a PyTuple().

https://github.com/python/cpython/blob/29acc08c8dad664cd5713cb392e5beba65724c10/Modules/_pickle.c#L6964

https://github.com/python/cpython/blob/29acc08c8dad664cd5713cb392e5beba65724c10/Objects/call.c#L460-L473

This means that any non-tuple iterator being used as the arguments passed into the function will cause C _pickle to throw an error, but Python pickle deserialization to unfold just fine.

payload:      b'cbuiltins\nprint\n}R.'

pickle:
None
_pickle.c:    FAILURE argument list must be a tuple
pickletools:
    0: c    GLOBAL     'builtins print'
   16: }    EMPTY_DICT
   17: R    REDUCE
   18: .    STOP
highest protocol among opcodes = 1

I think the easiest way to remedy the discrepancy is to explicitly type check the args parameter in pickle.py's load_reduce() function.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-144419

Empieza por Lib/pickle.py's load_reduce() y compara su gestión de argumentos con Modules/_pickle.c y el comportamiento de PyObject_CallObject() al que se hace referencia en Objects/call.c. Revisa el PR enlazado gh-144419 y las pruebas existentes de pickle; se considera terminado cuando Python pickle y _pickle gestionen de forma coherente el caso de argumento que no es una tupla indicado.