Code blocks S->M are rendered incorrectly

[twouters]

Code blocks sent from Slack to Matrix are using different line breaks (<br/>) than those sent from Matrix (from Element web/desktop) (\n).

Message sent from Element:

Message received from Slack:

The formatted_body differs:

Message sent from Element:

    "formatted_body": "<pre><code>code block\nline 2\nline 3\n</code></pre>\n",

Message received from Slack:

    "formatted_body": "<pre><code>code block slack-&gt;matrix<br/>line 2<br/>line 3</code></pre>",