text improvements and add versionadded info

Author: MrYamous

notifier.rst

@@ -762,11 +762,15 @@ typical alert levels, which you can implement immediately using:
 Testing Notifier
 ----------------
 
-With FrameworkBundle Symfony provide a :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\NotificationAssertionsTrait`
+Symfony provides a :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\NotificationAssertionsTrait`
 which provide useful methods for testing your Notifier implementation.
-You can benefit from this class by using it directly or extending :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\KernelTestCase`.
+You can benefit from this class by using it directly or extending the :class:`Symfony\\Bundle\\FrameworkBundle\\Test\\KernelTestCase`.
 
-See :ref:`testing documentation <notifier-assertions>` for list of availables assertions.
+See :ref:`testing documentation <notifier-assertions>` for the list of available assertions.
+
+.. versionadded:: 6.2
+
+    The Notifier assertions were introduced in Symfony 6.2.
 
 Disabling Delivery
 ------------------