Addresses review comments on gh-134570

Author: garry-cairns

Doc/library/unittest.rst

@@ -1178,8 +1178,7 @@ Test cases
       .. versionadded:: 3.4
 
       .. versionchanged:: next
-         Now accepts a *formatter* so your assertions can match
-         a custom format where you are using one.
+         Now accepts a *formatter* to control how messages are formatted.
 
    .. method:: assertNoLogs(logger=None, level=None)
 

Doc/whatsnew/3.15.rst

@@ -296,7 +296,7 @@ unittest
 
 * Lets users specify formatter in TestCase.assertLogs.
   :func:`unittest.TestCase.assertLogs` will now accept a formatter
-  argument so your assertions can match a custom format where you are using one.
+  to control how messages are formatted.
   (Contributed by Garry Cairns in :gh:`134567`.)