Markdown module regression in support for multiple codeblocks in same document

### Impacted plugin

Jetpack

### Quick summary

At some point, the markdown module in the Jetpack plugin broke its handling of multiple consecutive code blocks consisting of \`\`\` in \ tags, lumping together the non-contiguous blocks instead of treating them separately.

Example of correct behavior before (reproducible now only by disabling the markdown plugin in Jetpack):


Versus how it is rendered now after enabling markdown support then updating the post (under 13.1.1):


This may or may not have been a regression introduced after 12.9.3 (which is the version I upgraded from, but it's hard to say because I don't know if I saved the post under 12.9.3 or not).

### Steps to reproduce

You can reproduce the bug by creating a post with the contents of this article:
[article.txt](https://github.com/Automattic/jetpack/files/14227513/article.txt)

### A clear and concise description of what you expected to happen.

Separate code blocks should be rendered, using the \ tags, not the \`\`\` within it.

### What actually happened

The opening \ tag continues past the ending \ tag.

### Impact

One

### Available workarounds?

No and the platform is unusable

### Platform (Simple and/or Atomic)

Self-hosted

### Logs or notes

_No response_

Start with the Jetpack markdown module and reproduce the issue using the linked article.txt contents in a self-hosted post. Confirm that consecutive non-contiguous code blocks produce separate

 elements and that the opening tag does not continue past its matching closing tag.

Written by the indexing model from the issue text.