Update version to 3.2.1 and fix whatsnew (#4635)

Author: lbdreyer

docs/src/whatsnew/3.2.rst

@@ -25,8 +25,8 @@ This document explains the changes made to Iris for this release
    any issues or feature requests for improving Iris. Enjoy!
 
 
-v3.2.1 |build_date| [unreleased]
-********************************
+v3.2.1 (11 Mar 2022)
+====================
 
 .. dropdown:: :opticon:`alert` v3.2.1 Patches
    :container: + shadow
@@ -48,10 +48,6 @@ v3.2.1 |build_date| [unreleased]
       :attr:`~iris.coords.Coord.bounds` array for a scalar
       :class:`~iris.coords.Coord`. (:pull:`4610`).
 
-   💼 **Internal**
-
-   #. N/A
-
 
 📢 Announcements
 ================

lib/iris/__init__.py

@@ -108,7 +108,7 @@ def callback(cube, field, filename):
 
 
 # Iris revision.
-__version__ = "3.2.0.post0"
+__version__ = "3.2.1"
 
 # Restrict the names imported when using "from iris import *"
 __all__ = [