[libc++][doc] Fixes building the release notes.

mordante · mordante · commit 5623b06f30e5 · 2024-07-23T18:42:03.000+02:00
This libc++ 19 release notes are not longer the active notes and need to
be hidden to avoid build errors.
diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst
@@ -5,7 +5,7 @@
     :hidden:
 
     ReleaseNotes/18
-    ReleaseNotes/20
+    ReleaseNotes/19
 
 .. The release notes are in versioned files, but we make sure to keep publishing
 .. them in an unversioned ReleaseNotes.html page for external sites to reference.
