Return failed instead of raising an error when an include_vars file is missing

Fixes #18508

(cherry picked from commit 937d872f4b)

lib/ansible/plugins/action/include_vars.py

@@ -137,8 +137,8 @@ class ActionModule(ActionBase):
                     results.update(updated_results)
 
             except AnsibleError as e:
+                failed = True
                 err_msg = to_native(e)
-                raise AnsibleError(err_msg)
 
         if self.return_results_as_name:
             scope = dict()