Bug 473940

SUMMARY
Code blocks inside of ``` are still interpreted as Markdown with only the Monospace font applied. For example, a comment inside a code block starting with # is rendered as a header. Also newlines are not kept like in normal Markdown rendering.

STEPS TO REPRODUCE
Write a code block like this:
---START OF EXAMPLE MARKDOWN---
### Culling
Do we need culling? That is, shut down notebooks when the user has long ago left? Or do we expect students to run sessions overnight?

Relevant options for `/opt/jupyterhub/etc/jupyterhub/jupyterhub_config.py`:

```
# shutdown the server after no activity for 20 minutes
c.NotebookApp.shutdown_no_activity_timeout = 20 * 60
# shutdown kernels after no activity for 10 minutes
c.MappingKernelManager.cull_idle_timeout = 10 * 60
# Check every minute
c.MappingKernelManager.cull_interval = 60
# cull connected (e.g. Browser tab open)
c.MappingKernelManager.cull_connected = True
```

## Monitoring

Prometheus allows for monitoring of the cluster health
---END OF EXAMPLE MARKDOWN---

OBSERVED RESULT
Inside the rendered code block, newlines disappear and lines starting with # are being rendered as headers.


EXPECTED RESULT
Code block should not be rendered as markdown but show the code exactly as is.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 23.08.0
KDE Frameworks Version: 5.109.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
I think this started happening after the update to 23.08.0 so it's very recent.