[3.14] Emend an error in `string.templatelib` example output (GH-137890) (#137892)

Emend an error in ``string.templatelib`` example output (GH-137890)
(cherry picked from commit 8e3244d39b)

Co-authored-by: Christoph Walcher <christoph-wa@gmx.de>

Doc/library/string.templatelib.rst

@@ -34,7 +34,7 @@ To write a t-string, use a ``'t'`` prefix instead of an ``'f'``, like so:
    >>> pi = 3.14
    >>> t't-strings are new in Python {pi!s}!'
    Template(
-      strings=('t-strings are new in Python ', '.'),
+      strings=('t-strings are new in Python ', '!'),
       interpolations=(Interpolation(3.14, 'pi', 's', ''),)
    )