minor #10993 Use "index" instead of "indexAction" (superbull)

This PR was merged into the 4.2 branch.

Discussion
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Use "index" instead of "indexAction"

Wrong controller action name.

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Commits
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68d67a5 Use "index" instead of "indexAction"

Author: javiereguiluz

create_framework/separation_of_concerns.rst

@@ -138,7 +138,7 @@ Don't forget to update the ``example.com/src/app.php`` file accordingly::
 
     $routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', [
         'year' => null,
-        '_controller' => 'Calendar\Controller\LeapYearController::indexAction',
+        '_controller' => 'Calendar\Controller\LeapYearController::index',
     ]));
 
 To sum up, here is the new file layout: