pythonGH-94808: Cover handling non-finite numbers from round when ndigits is provided (pythonGH-94860)

(cherry picked from commit 625ba9b)

Co-authored-by: Michael Droettboom <mdboom@gmail.com>

Author: mdboom

Lib/test/test_float.py

@@ -832,6 +832,11 @@ def test_inf_nan(self):
         self.assertRaises(TypeError, round, NAN, "ceci n'est pas un integer")
         self.assertRaises(TypeError, round, -0.0, 1j)
 
+    def test_inf_nan_ndigits(self):
+        self.assertEqual(round(INF, 0), INF)
+        self.assertEqual(round(-INF, 0), -INF)
+        self.assertTrue(math.isnan(round(NAN, 0)))
+
     def test_large_n(self):
         for n in [324, 325, 400, 2**31-1, 2**31, 2**32, 2**100]:
             self.assertEqual(round(123.456, n), 123.456)