bpo-30004: Fix the code example of using group in Regex Howto Docs (GH-4443) (GH-4555)

The provided code example was supposed to find repeated words, however it returned false results.
(cherry picked from commit 610e5afd)

Doc/howto/regex.rst

@@ -840,7 +840,7 @@ backreferences in a RE.
 
 For example, the following RE detects doubled words in a string. ::
 
-   >>> p = re.compile(r'(\b\w+)\s+\1')
+   >>> p = re.compile(r'\b(\w+)\s+\1\b')
    >>> p.search('Paris in the the spring').group()
    'the the'
 
@@ -947,9 +947,9 @@ number of the group.  There's naturally a variant that uses the group name
 instead of the number. This is another Python extension: ``(?P=name)`` indicates
 that the contents of the group called *name* should again be matched at the
 current point.  The regular expression for finding doubled words,
-``(\b\w+)\s+\1`` can also be written as ``(?P<word>\b\w+)\s+(?P=word)``::
+``\b(\w+)\s+\1\b`` can also be written as ``\b(?P<word>\w+)\s+(?P=word)\b``::
 
-   >>> p = re.compile(r'(?P<word>\b\w+)\s+(?P=word)')
+   >>> p = re.compile(r'\b(?P<word>\w+)\s+(?P=word)\b')
    >>> p.search('Paris in the the spring').group()
    'the the'