minor #17298 [DependencyInjection] Fix docs referencing an incorrect PHP function (Toflar)

This PR was submitted for the 6.1 branch but it was merged into the 5.4 branch instead.

Discussion
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[DependencyInjection] Fix docs referencing an incorrect PHP function

Looks like some leftover? At least, there is no `ref` function 🤔

Commits
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f0048ef Fix docs referencing an incorrect PHP function

Author: javiereguiluz

service_container/service_subscribers_locators.rst

@@ -293,10 +293,10 @@ argument of type ``service_locator``:
 
             $services->set(CommandBus::class)
                 ->args([service_locator([
-                    'App\FooCommand' => ref('app.command_handler.foo'),
-                    'App\BarCommand' => ref('app.command_handler.bar'),
+                    'App\FooCommand' => service('app.command_handler.foo'),
+                    'App\BarCommand' => service('app.command_handler.bar'),
                     // if the element has no key, the ID of the original service is used
-                    ref('app.command_handler.baz'),
+                    service('app.command_handler.baz'),
                 ])]);
         };