Update instructions/a11y.instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: mfairchild365

instructions/a11y.instructions.md

@@ -270,7 +270,7 @@ All graphics include `img`, `svg`, icon fonts, and emojis.
 - Use semantic navigation: `<nav>` with lists and links.
 - Do not use `role="menu"` / `role="menubar"` for site navigation.
 - For expandable navigation:
-  -  Include button elements to toggle navigation and/or sub-navigations. Use `aria-expanded` on the button to indicate state.
+  - Include button elements to toggle navigation and/or sub-navigations. Use `aria-expanded` on the button to indicate state.
   - `Escape` MAY close open sub-navigations.
 
 ## Tables and grids