Update spec/grape/dsl/inside_route_spec.rb

Co-authored-by: Copilot <[email protected]>

Author: ericproulx

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 #### Features
 
+* [#2574](https://github.com/ruby-grape/grape/pull/2574) Reduce ActiveSupport::Concern usage - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 #### Fixes

spec/grape/dsl/inside_route_spec.rb

@@ -54,7 +54,7 @@ def namespace_inheritable_hash
       end
 
       def namespace_stackable_hash
-        @namespace_stackable_hash ||= Hash.new { [] }
+        @namespace_stackable_hash ||= Hash.new { |h, k| h[k] = [] }
       end
 
       def namespace_stackable_with_hash_hash