Cleanup: prefer 'arg' over 'params' for sphinx documentation

While both are supported, 'arg' is in more common use so prefer it.

source/blender/python/mathutils/mathutils_Vector.c

@@ -3188,7 +3188,7 @@ PyDoc_STRVAR(vector_doc,
              "\n"
              "   This object gives access to Vectors in Blender.\n"
              "\n"
-             "   :param seq: Components of the vector, must be a sequence of at least two\n"
+             "   :arg seq: Components of the vector, must be a sequence of at least two\n"
              "   :type seq: sequence of numbers\n");
 PyTypeObject vector_Type = {
     PyVarObject_HEAD_INIT(NULL, 0)