[Console] Minor tweaks

Author: alexandre-daubois

console/calling_commands.rst

@@ -27,7 +27,7 @@ method)::
     {
         // ...
 
-        protected function execute(InputInterface $input, OutputInterface $output): void
+        protected function execute(InputInterface $input, OutputInterface $output): int
         {
             $command = $this->getApplication()->find('demo:greet');
 

console/verbosity.rst

@@ -69,7 +69,7 @@ level. For example::
                 OutputInterface::VERBOSITY_VERBOSE
             );
 
-            return 0;
+            return Command::SUCCESS;
         }
     }