Collapsible Markdown formatted weirdly

Summary

While <details> works perfectly when creating issues, it doesn't in GitLab Readme.

Steps to reproduce

Try these on any README.md project on GitLab

## Backend

<details>
  <summary>Features:</summary>
</pre>

### Feature breakdown
* [x] Automatically create REST API from Models with [`finale-rest`](https://github.com/tommybananas/finale)
* [x] Code style helper
  * [x] Import module supported by default
  * [x] ESlint
  * [x] Prettier
* [x] Code organization, we follow these conventions
  * [x] `models` folder -> contains database models and `sequelize` instance 
  * [x] `rest` folder -> contains `final-rest` bootstrapping code
  * [x] `app.js` file -> contains express bootstrapping code
  * [x] root `index.js` file -> contains instantiation of express app
* [ ] Testing with [`Mocha`](https://mochajs.org/)
* [ ] Development Environment
  * [ ] Use `docker-compose` for local development dependencies (e.g. PostgresSQL)
  * [ ] Commit hook with husky
  * [ ] Nodemon file watcher for development quick iteration
* [ ] Operations
  * [ ] Config using environment variables
  * [ ] Ping and health check endpoint
  * [ ] Dockerfile for container deployment
  * [ ] CI using GitLab
  * [ ] CD using Kubernetes
  * [ ] Uses JSON log by default
  * [ ] Sequelize log in JSON
  * [ ] API log requests
  * [ ] Graceful shutdown upon restart and SIGKILL
  * [ ] Error handling middleware (optional)
  * [ ] Sentry crash reporting by default
  * [ ] CLI for operational stuff
* [ ] Authentication using Auth0

</pre>
</details>

Example Project

N/A

What is the current bug behavior?

You'll see

What is the expected correct behavior?

Clear formatting.

Relevant logs and/or screenshots

N/A

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:env:info)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)