Fix OKR creation

What does this MR do and why?

Fixes OKR creation when :use_iid_in_work_items_path feature flag is on.

Requires :okrs_mvc.

Screenshots or screen recordings

Before	After
	Objective_7___Objective___gitlab-org_gitlab-shell

How to set up and validate locally

1. Open rails console by running bin/rails console within GDK directory.
2. Enable the feature flag :use_iid_in_work_items_path on a project; Feature.enable(:use_iid_in_work_items_path, Project.find_by_full_path('gitlab-org/gitlab-test')).
3. Enable the feature flag :okrs_mvc on the same project; Feature.enable(:okrs_mvc, Project.find_by_full_path('gitlab-org/gitlab-test')).
4. Visit issues list page for the project by navigating to http://gdk.test:3000/gitlab-org/gitlab-test/-/issues.
5. Create an objective by clicking on dropdown button next to New issue and selecting New objective from the dropdown.
6. Once objective is created, click on it to visit its Work Item page, you should be able to see Tree View below the description.
7. Use Add dropdown button create/add objectives and key results.

MR acceptance checklist

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