Update whichmodule tests in cloudpickle to work with numpy 2.2.

[petrmitrichev]

1. test_non_module_object_passing_whichmodule_test was not testing what it was supposed to test, because after some refactoring passing "name" to "_whichmodule" became mandatory for the module lookup to occur. Changed the test to pass "func" name.

2. test_importing_multiprocessing_does_not_impact_whichmodule was no longer testing what it was supposed to test after the numpy 2.2 release which caused the numpy symbols to have a module attached, and therefore the module lookup was no longer occuring (and the test was failing). Changed the test to avoid dependency on numpy, instead testing with our own function.

[petrmitrichev]

To clarify, when I write "was not testing what it was supposed to test", I mean that:

1. test_non_module_object_passing_whichmodule_test was passing even with this line commented out.
2. test_importing_multiprocessing_does_not_impact_whichmodule was failing with numpy 2.2 as the new return value became just "numpy". But adding "numpy" to the list of valid answers would make it pass even with this line commented out.

[ogrisel]

I agree, this is an improvement in test maintainability and correctness.

Thanks for the fix.