DOC: Update mypy version in whatsnew (#39419)

Author: phofl

doc/source/whatsnew/v1.3.0.rst

@@ -117,7 +117,7 @@ If installed, we now require:
 +-----------------+-----------------+----------+---------+
 | pytest (dev)    | 5.0.1           |          |         |
 +-----------------+-----------------+----------+---------+
-| mypy (dev)      | 0.790           |          |    X    |
+| mypy (dev)      | 0.800           |          |    X    |
 +-----------------+-----------------+----------+---------+
 
 For `optional libraries <https://pandas.pydata.org/docs/getting_started/install.html>`_ the general recommendation is to use the latest version.