Issue #18548: Fix unittest.TestSuite() example

Initial patch by py.user.
diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index 0fc02c4..e5646ae 100644
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -352,7 +352,7 @@
 
    import unittest
 
-   class SimpleWidgetTestCase(unittest.TestCase):
+   class WidgetTestCase(unittest.TestCase):
        def setUp(self):
            self.widget = Widget('The widget')
 
@@ -379,7 +379,7 @@
 
    import unittest
 
-   class SimpleWidgetTestCase(unittest.TestCase):
+   class WidgetTestCase(unittest.TestCase):
        def setUp(self):
            self.widget = Widget('The widget')