bpo-32735: Fix typo in f-strings datetime format specifier example (GH-5464)

The f-string example for using datetime format specifier does not match the given output.
Changed the format from %b to %B so it matches the output of "January".

Author: csabella

Doc/reference/lexical_analysis.rst

@@ -676,7 +676,7 @@ Some examples of formatted string literals::
    >>> f"result: {value:{width}.{precision}}"  # nested fields
    'result:      12.35'
    >>> today = datetime(year=2017, month=1, day=27)
-   >>> f"{today:%b %d, %Y}"  # using date format specifier
+   >>> f"{today:%B %d, %Y}"  # using date format specifier
    'January 27, 2017'
    >>> number = 1024
    >>> f"{number:#0x}"  # using integer format specifier