fix(examples): use html_url in the large-list iteration taskflow

The repeat_prompt template referenced `result.url`, but the GitHub tool returns
pull request objects with `html_url` (no `url`), so rendering failed under
StrictUndefined. Reference `result.html_url` to match the tool output.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: anticomputer

examples/taskflows/example_large_list_result_iter.yaml

@@ -24,4 +24,4 @@ taskflow:
       agents:
         - seclab_taskflow_agent.personalities.assistant
       user_prompt: |
-        Echo this:  The title is {{ result.title }} and the url is {{ result.url }}.
+        Echo this:  The title is {{ result.title }} and the url is {{ result.html_url }}.