Extend rustdoc hashtag prepended line test

Author: GuillaumeGomez

src/librustdoc/html/markdown/tests.rs

@@ -343,6 +343,14 @@ fn test_ascii_with_prepending_hashtag() {
 #..#.#....#....#....#..#.
 #..#.#....#....#....#..#.
 #..#.####.####.####..##..
+</code></pre></div>",
+    );
+    t(
+        r#"```markdown
+# hello
+```"#,
+        "<div class=\"example-wrap\"><pre class=\"language-markdown\"><code>\
+# hello
 </code></pre></div>",
     );
 }