Fix nested ordered task list styling in issue description

What does this MR do and why?

This MR fixes nested ordered task list styling, which can be seen in #371275 (closed)

Changelog: fixed

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Go to issue page (e.g. http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/1)
2. Test the issue

Markup used in testing

- item
  1. [ ] item
  1. [ ] item
     1. [ ] item
     1. [ ] item
- item

---

1. item
   1. [ ] item
   1. [ ] item
      1. [ ] item
      1. [ ] item
1. item

---

- [ ] item
  1. [ ] item
  1. [ ] item
     1. [ ] item
     1. [ ] item
- [ ] item

---

1. [ ] item
   1. [ ] item
   1. [ ] item
      1. [ ] item
      1. [ ] item
1. [ ] item

---

1. [ ] item
1. [ ] item
1. [ ] item

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.