[3.13] typing docs: Fix formatting issue (GH-119210) (#119212)

typing docs: Fix formatting issue (GH-119210)
(cherry picked from commit 72d07dd)

Co-authored-by: David Foster <david@dafoster.net>

Doc/library/typing.rst

@@ -2546,7 +2546,7 @@ types.
          ``__required_keys__`` and ``__optional_keys__`` rely on may not work
          properly, and the values of the attributes may be incorrect.
 
-   Support for :data:`ReadOnly` is reflected in the following attributes::
+   Support for :data:`ReadOnly` is reflected in the following attributes:
 
    .. attribute:: __readonly_keys__