bpo-33750: Reset thread-local context precision in test_round(). (#7355)

Lib/test/test_decimal.py

@@ -4454,9 +4454,9 @@ class Coverage(unittest.TestCase):
     def test_round(self):
         # Python3 behavior: round() returns Decimal
         Decimal = self.decimal.Decimal
-        getcontext = self.decimal.getcontext
+        localcontext = self.decimal.localcontext
 
-        c = getcontext()
+        with localcontext() as c:
             c.prec = 28
 
             self.assertEqual(str(Decimal("9.99").__round__()), "10")
@@ -5410,7 +5410,7 @@ class CWhitebox(unittest.TestCase):
 
             # SSIZE_MIN
             x = (1, (), -sys.maxsize-1)
-            self.assertEqual(str(c.create_decimal(x)), '-0E-1000026')
+            self.assertEqual(str(c.create_decimal(x)), '-0E-1000007')
             self.assertRaises(InvalidOperation, Decimal, x)
 
             x = (1, (0, 1, 2), -sys.maxsize-1)