[libc++][doc] Fixes a formating issue.

NOKEYCHECK=True
GitOrigin-RevId: e8fdf8e31bd5e1fe034c77da2ec97ff1e5dd5fb1
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index a04eacb..2b16ec5 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -68,7 +68,7 @@
 
   - C++20: ``chrono``
   - C++2b: ``algorithm``, ``array``, ``atomic``, ``bit``, ``chrono``,
-    ``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdarg`, ``cstddef``,
+    ``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdarg``, ``cstddef``,
     ``cstdint``, ``cstdlib``, ``cstring``, ``ctime``, ``exception``,
     ``functional``, ``initializer_list``, ``iosfwd``, ``iterator``, ``limits``,
     ``memory``, ``new``, ``numeric``, ``optional``, ``ratio``, ``stdexcept``,