Add the missing versionadded directive

Author: javiereguiluz

testing.rst

@@ -1090,6 +1090,10 @@ Mailer Assertions
     Asserts that the subject of the given email does (not) contain the
     expected subject.
 
+.. versionadded:: 7.4
+
+    The ``assertEmailAddressNotContains()`` assertion was introduced in Symfony 7.4.
+
 Notifier Assertions
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