Describe the bug

When an unknown (unregistered) language is passed to a code block, the component falls back to rendering passed children as plain text with no Markdown formatting applied.

Impact and severity

This is a user-facing issue that has been reported internally.

Environment and versions

• EUI version: 102.2.0
• React version: 18.2
• Kibana version (if applicable): N/A
• Browser: N/A
• Operating System: N/A

To Reproduce

Steps to reproduce the behavior:

1. Go to https://eui.elastic.co/docs/components/editors-and-syntax/markdown/format/#built-in-plugins
2. Edit the markdownContent variable value to:

   # Hello, World!
   ~~~blah
   console.log(123);
   ~~~
   

3. See the whole Markdown content being rendered as plain text with no Markdown formatting applied to either the heading or the code block