marshal tests are sloppy with error checking

[iritkatriel]

pymarshal_write_long_to_file and pymarshal_write_object_to_file pretend that PyMarshal_WriteLongToFile/PyMarshal_WriteObjectToFile can set an error.

pymarshal_read_last_object_from_file and pymarshal_read_object_from_file don't check for errors so they can call Py_BuildValue with a NULL arg.

Linked PRs

• gh-104645: fix error handling in marshal tests #104646
• [3.11] gh-104645: fix error handling in marshal tests (GH-104646) #104663