use assert[Not]In where appropriate

A patch from Dave Malcolm.
diff --git a/Lib/test/test_dictviews.py b/Lib/test/test_dictviews.py
index 4fee755..4d12647 100644
--- a/Lib/test/test_dictviews.py
+++ b/Lib/test/test_dictviews.py
@@ -24,10 +24,10 @@
         self.assertNotEqual(keys, {1, "b"})
         self.assertNotEqual(keys, {1})
         self.assertNotEqual(keys, 42)
-        self.assertTrue(1 in keys)
-        self.assertTrue("a" in keys)
-        self.assertTrue(10 not in keys)
-        self.assertTrue("Z" not in keys)
+        self.assertIn(1, keys)
+        self.assertIn("a", keys)
+        self.assertNotIn(10, keys)
+        self.assertNotIn("Z", keys)
         self.assertEqual(d.keys(), d.keys())
         e = {1: 11, "a": "def"}
         self.assertEqual(d.keys(), e.keys())
@@ -44,13 +44,13 @@
         self.assertNotEqual(items, {(1, 10), ("a", "def")})
         self.assertNotEqual(items, {(1, 10)})
         self.assertNotEqual(items, 42)
-        self.assertTrue((1, 10) in items)
-        self.assertTrue(("a", "ABC") in items)
-        self.assertTrue((1, 11) not in items)
-        self.assertTrue(1 not in items)
-        self.assertTrue(() not in items)
-        self.assertTrue((1,) not in items)
-        self.assertTrue((1, 2, 3) not in items)
+        self.assertIn((1, 10), items)
+        self.assertIn(("a", "ABC"), items)
+        self.assertNotIn((1, 11), items)
+        self.assertNotIn(1, items)
+        self.assertNotIn((), items)
+        self.assertNotIn((1,), items)
+        self.assertNotIn((1, 2, 3), items)
         self.assertEqual(d.items(), d.items())
         e = d.copy()
         self.assertEqual(d.items(), e.items())