minor #6685 NullOutput should be passed to $command->run() (Ma27)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #6685).

Discussion
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NullOutput should be passed to $command->run()

as $command#execute() is protected, the NullOutput should be passed to $command#run() as that's the public method being invoked when calling an existing command.

Commits
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5796c81 NullOutput should be passed to $command->run()

Author: xabbuh

components/console/introduction.rst

@@ -552,7 +552,7 @@ returns the returned code from the command (return value from command's
 
     If you want to suppress the output of the executed command, pass a
     :class:`Symfony\\Component\\Console\\Output\\NullOutput` as the second
-    argument to ``$command->execute()``.
+    argument to ``$command->run()``.
 
 .. caution::