A handful of monthly post fixes

[lqd]

A few fixes for some of the issues I mentioned on zulip.

• some double escaping
• replace the "Help needed" image causing the broken layout on the rust blog with just text
• a silly typo on my part
• looking for the most recent TL;DR comment was incorrect
• the documentation for cargo rpg updates was outdated/duplicated, and I've also documented the start date which is always important when generating the blog post.
• fix the "Help wanted" regex to allow for the option list markers that are part of the suggested update template pings
• ignore empty "Help wanted" updates since that happened

This also fixes the status of the cargo script goal — though I think I fixed the 2025h1 goal count for the monthly post when fixing its GH milestone rather than via this status, but this change should fix the goal count on the website itself.

Rendered