ignore a C code example

lib/src/string.rs

@@ -411,7 +411,7 @@ impl CList for TCStringList {
 ///
 /// For example:
 ///
-/// ```
+/// ```text
 /// char *url = get_item_url(..); // dynamically allocate C string
 /// tc_task_annotate(task, tc_string_borrow(url)); // TCString created, passed, and freed
 /// free(url); // string is no longer referenced and can be freed