Fix randomly failing doctest

This is a "correct" fix because the `DeprecationWarning` is unrelated to
the test.

Author: grhkm21

src/sage/rings/number_field/number_field_element_quadratic.pyx

@@ -2399,8 +2399,6 @@ cdef class NumberFieldElement_quadratic(NumberFieldElement_absolute):
             ....:    assert round(a+b*sqrt(2.)) == round(a+b*sqrt2), (a, b)
             ....:    assert round(a+b*sqrt(3.)) == round(a+b*sqrt3), (a, b)
             ....:    assert round(a+b*sqrt(5.)) == round(a+b*sqrt5), (a, b)
-            doctest...: DeprecationWarning: the default rounding for rationals, currently `away`, will be changed to `even`.
-            See https://github.com/sagemath/sage/issues/35473 for details.
         """
         n = self.floor()
         test = 2 * (self - n).abs()