fix(bleach-to-nh3): update os_message test assertion for nh3 link output

nh3 adds rel="noopener noreferrer" to links; update assertion to match.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: valentijnscholten

unittests/test_os_message.py

@@ -43,7 +43,7 @@ def test_headline_inline_markdown(self):
         text = "# Read the **release notes** at [link](https://example.com)\n"
         result = os_message.parse_os_message(text)
         self.assertIn("<strong>release notes</strong>", result["message"])
-        self.assertIn('<a href="https://example.com">link</a>', result["message"])
+        self.assertIn('<a href="https://example.com" rel="noopener noreferrer">link</a>', result["message"])
         self.assertIsNone(result["expanded_html"])
 
     def test_headline_strips_disallowed_html(self):