Code block within spoiler gives different result than shown in preview

Describe the bug
A code block within a spoiler block gives a different result than shown when looking at the Markdown preview before posting/saving an answer.

To Reproduce

When using the following markdown in the answer editor:

>! ```python
>! if True:
>!     print "Hello World"
>! ```

It shows this result when viewing the preview during editing (with the multi-line code):

Screenshot is of this answer (it's currently deleted, because it's not yet working as expected)

Note: The markdown only shows as shown in the screenshot when editing an answer and viewing the live markdown preview/result (WYSIWYG), not when editing a question.

Related question

Expected behavior

I would expect the result to look like the preview after posting/saving. I also think that being able to post a code block within a spoiler is useful on https://codegolf.stackexchange.com

Desktop (please complete the following information):

• OS: Windows 10, 21H2
• Browser: Chromium 105

Reproduce the markdown in the answer editor and compare the live preview with the result after posting or saving. Trace the answer editor's spoiler and code-block rendering paths; done when a code block inside a spoiler renders the same way in preview and in the saved answer.