Goof: Make Slack wrapper use double tildes ~~ to encode a strikethrough

See also "Markdown, Strikethrough, and Slack" [1].

[1] https://daringfireball.net/linked/2015/11/05/markdown-strikethrough-slack

Author: amotl

CHANGES.md

@@ -1,6 +1,8 @@
 # Changelog
 
 ## In progress
+- Goof: Made Slack wrapper use double tildes `~~` to encode a ~~strikethrough~~,
+  see also [Markdown, Strikethrough, and Slack].
 
 ## v0.6.1, 2025-04-01
 - Shell/Notify: Added reference about caveats page to weekly report's preamble
@@ -106,3 +108,6 @@
   ```shell
   rapporto github activity --organization=python --author=AA-Turner --when="2025-01-01..2025-01-31"
   ```
+
+
+[Markdown, Strikethrough, and Slack]: https://daringfireball.net/linked/2015/11/05/markdown-strikethrough-slack

src/rapporto/source/github/attention.py

@@ -101,7 +101,7 @@ def markdown(self):
             )
             link = f"[{title}]({item.html_url})"
             if is_closed:
-                line = f"- ~{link}~"
+                line = f"- ~~{link}~~"
             else:
                 line = f"- {link}"
             # line = f"- {link} {', '.join(labels)}"