[DI] add syntax to stack decorators

Author: nicolas-grekas

DependencyInjection/Compiler/UnusedTagsPass.php

@@ -38,6 +38,7 @@ class UnusedTagsPass implements CompilerPassInterface
         'container.service_locator',
         'container.service_locator_context',
         'container.service_subscriber',
+        'container.stack',
         'controller.argument_value_resolver',
         'controller.service_arguments',
         'data_collector',