Fix MD024 lint failure by enabling siblings_only for duplicate headings

Co-authored-by: Malcolmnixon <1863707+Malcolmnixon@users.noreply.github.com>

Author: Copilot

.markdownlint-cli2.jsonc

@@ -4,6 +4,7 @@
     "MD003": { "style": "atx" },
     "MD007": { "indent": 2 },
     "MD013": { "line_length": 120 },
+    "MD024": { "siblings_only": true },
     "MD025": false,
     "MD033": false,
     "MD041": false