When a Markdown ordered list has blank lines between items (common in
LLM-authored content), the list run loop breaks on each blank line.
Slack numbers each rich_text_list independently, so N items produce N
lists each starting at 1.
Skip blank lines inside the list run as soft separators instead of
breaking, so ordered items stay in one rich_text_list and Slack renders
the correct numbering.
Fixes#57076
d3c8a155cb