fix rendering of code block example

we want it to be rendered as markdown source

content/en/docs/customisation/themes.md

@@ -154,10 +154,10 @@ former won't escape the theme.
 
 MFM code blocks like these:
 
-  <!-- markdownlint-disable-next-line MD048 -->
-  ```ts
-  const foo=1;
-  ```
+<!-- markdownlint-disable-next-line MD046 -->
+    ```ts
+    const foo=1;
+    ```
 
 are rendered with syntax highlighting provided by the
 [Shiki](https://shiki.style/) package. You can provide your own styles