bpo-47235: Note where a typo is intentional in code. (GH-32348)

People keep popping up reporting these as typos in the docs despite
being described as typos in the surrounding text.  Hopefully a comment
on the line itself makes it more obvious?

Arguably some of the typo examples are not using the "right" typo as the
"assret" one in particular is now detected by default due to how common
it was in actual code.  But I don't want to to typo chasing by changing
these examples to be other not yet auto-detected typos as they still
illustrate the point well enough.

Doc/library/unittest.mock.rst

@@ -2550,7 +2550,7 @@ your assertion is gone:
 
     >>> mock = Mock(name='Thing', return_value=None)
     >>> mock(1, 2, 3)
-    >>> mock.assret_called_once_with(4, 5, 6)
+    >>> mock.assret_called_once_with(4, 5, 6)  # Intentional typo!
 
 Your tests can pass silently and incorrectly because of the typo.
 
@@ -2570,7 +2570,7 @@ attributes on the mock that exist on the real class:
 
     >>> from urllib import request
     >>> mock = Mock(spec=request.Request)
-    >>> mock.assret_called_with
+    >>> mock.assret_called_with  # Intentional typo!
     Traceback (most recent call last):
      ...
     AttributeError: Mock object has no attribute 'assret_called_with'
@@ -2582,7 +2582,7 @@ with any methods on the mock:
 
     >>> mock.has_data()
     <mock.Mock object at 0x...>
-    >>> mock.has_data.assret_called_with()
+    >>> mock.has_data.assret_called_with()  # Intentional typo!
 
 Auto-speccing solves this problem. You can either pass ``autospec=True`` to
 :func:`patch` / :func:`patch.object` or use the :func:`create_autospec` function to create a
@@ -2625,7 +2625,7 @@ any typos in our asserts will raise the correct error::
 
     >>> req.add_header('spam', 'eggs')
     <MagicMock name='request.Request().add_header()' id='...'>
-    >>> req.add_header.assret_called_with
+    >>> req.add_header.assret_called_with  # Intentional typo!
     Traceback (most recent call last):
      ...
     AttributeError: Mock object has no attribute 'assret_called_with'