pythongh-105184: document that marshal functions can fail and need to…

… be checked with PyErr_Occurred

Doc/c-api/marshal.rst

@@ -25,12 +25,16 @@ unmarshalling.  Version 2 uses a binary format for floating point numbers.
    the least-significant 32 bits of *value*; regardless of the size of the
    native :c:expr:`long` type.  *version* indicates the file format.
 
+   This function can fail, in which case it sets the error indicator.
+   Use ``PyErr_Occurred()`` to check for that.
 
 .. c:function:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)
 
    Marshal a Python object, *value*, to *file*.
    *version* indicates the file format.
 
+   This function can fail, in which case it sets the error indicator.
+   Use ``PyErr_Occurred()`` to check for that.
 
 .. c:function:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)