bug(markdown) Adding code block around backticks doesn't work properly

[yellis]

To Reproduce

1. MD mode, type in 4 backticks
2. Highlight them, set codeblock
3. results in 3 lines with 3 backticks
4. This gets mangled when go to RT, turning into 2 empty code blocks. So this translation is a problem.
5. Going back to MD, ends up with 2 lines of 3 backticks, and empty line, and 2 lines of 3 backticks again (translation of the RT from step 4).

The MSE post points out several way to apply the codeblock to make this work, most practically in this case:

````
```
````

Which translates fine round-trip.

Expected behavior
Making this into a code block will do so in such a way that it can round trip and render properly

Screenshots

Desktop (please complete the following information):
Windows 11 Chrome 103

Additional context
https://meta.stackexchange.com/a/380356/51