Handle Wikipedia code blocks in /fetch command (#12780)

This PR extends the `/fetch` command with support for Wikipedia code
blocks.

Release Notes:

- N/A

crates/html_to_markdown/src/markdown_writer.rs

@@ -162,7 +162,7 @@ impl MarkdownWriter {
         }
 
         let text = text
-            .trim_matches(|char| char == '\n' || char == '\r')
+            .trim_matches(|char| char == '\n' || char == '\r' || char == '\t')
             .replace('\n', " ");
 
         self.push_str(&text);