[wwwdocs] Fix typo in libstdc++ release notes

[Jonathan Wakely <jwakely@redhat.com>]

The monadic ops for std::optional were in GCC 12, I meant to say
std::expected in the GCC 13 release notes.

---
 htdocs/gcc-13/changes.html | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index d9879d79..41a117b4 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -243,7 +243,7 @@ a work-in-progress.</p>
       <code>views::repeat</code>, <code>views::chunk_by</code>,
       <code>views::cartesian_product</code>, <code>views::as_rvalue</code>.
     </li>
-    <li>Monadic operations for <code>std::optional</code>.</li>
+    <li>Monadic operations for <code>std::expected</code>.</li>
     <li>Constexpr <code>std::bitset</code>, <code>std::to_chars</code>
       and <code>std::from_chars</code>.
     </li>
-- 
2.39.0