fix: Use endpoint.class instead of endpoint.inspect in error message

Some Grape versions have protected inspect methods on endpoint objects.
Use endpoint.class for the error message instead, which is simpler and
works reliably across all Grape versions (1.8.0, 2.1.3, 2.4.0, 3.0+).

This resolves failures when testing with Ruby 3.1.0 and Grape 2.1.3.

Author: numbata

lib/grape-swagger/token_owner_resolver.rb

@@ -16,7 +16,7 @@ def resolve(endpoint, method_name)
         helper_value = resolve_from_helpers(endpoint, method_name)
         return helper_value unless helper_value.equal?(UNRESOLVED)
 
-        raise Errors::TokenOwnerNotFound, "undefined method `#{method_name}` for #{endpoint.inspect}"
+        raise Errors::TokenOwnerNotFound, "undefined method `#{method_name}` for #{endpoint.class}"
       end
 
       def evaluate_proc(callable, token_owner)