Markdown rendering of double indented lists fails

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Summary

Double indented markdown lists fail to render properly: the double indent is at the same level as the single indent.

Steps to reproduce

Markdown source:

- X* One
- V Two
  - Indented
- O Three
  - Indented
    - Double Indented
    - Double Indented
    - Double Indented
    - Double Indented
  - Indented Too
    - Double Indented
    - Double Indented
    - Double Indented
- O Four
- O Five

It displays the same as:

- X* One
- V Two
  - Indented
- O Three
  - Indented
  - Double Indented
  - Double Indented
  - Double Indented
  - Double Indented
  - Indented Too
  - Double Indented
  - Double Indented
  - Double Indented
- O Four
- O Five

Example Project

https://gitlab.com/wiert.me/gitlab/issues/blob/master/unordered-list-indenting.md

What is the current bug behavior?

Actual rendering:

<ul dir="auto">
<li>X* One</li>
<li>V Two

<ul>
<li>Indented</li>
</ul>
</li>
<li>O Three

<ul>
<li>Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
<li>Indented Too</li>
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
</ul>
</li>
<li>O Four</li>
<li>O Five</li>
</ul>

What is the expected correct behavior?

Expected rendering:

<ul dir="auto">
<li>X* One</li>
<li>V Two

<ul>
<li>Indented</li>
</ul>
</li>
<li>O Three

<ul>
<li>Indented</li>
<ul dir="auto">
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
</ul>
<li>Indented Too</li>
<ul dir="auto">
<li>Double Indented</li>
<li>Double Indented</li>
<li>Double Indented</li>
</ul>
</ul>
</li>
<li>O Four</li>
<li>O Five</li>
</ul>

Relevant logs and/or screenshots

Actual rendering

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

N/A

Results of GitLab application Check

N/A

Possible fixes

N/A