minor #6288 Update factories.rst (velikanov)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #6288).

Discussion
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Update factories.rst

Wrong closing tag for "container" tag in first XML services definition

Commits
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7973328 Update factories.rst

Author: xabbuh

components/dependency_injection/factories.rst

@@ -55,7 +55,7 @@ factory class:
                     factory-class="NewsletterManagerFactory"
                     factory-method="createNewsletterManager" />
             </services>
-        </services>
+        </container>
 
     .. code-block:: php