Make QList::max_size() constexpr

Looks like it was just forgotten in the original patch.

Found in Qt 6.8 API review.

Amends 7ce6920aac.

Change-Id: Ibcc5ec8408b834f1271e632b804efdfb93f9203f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit d585c7c0a3e49ba841712ea0b4b19d307b34f249)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/tools/qlist.h

@@ -690,7 +690,7 @@ public:
     inline reference back() { return last(); }
     inline const_reference back() const noexcept { return last(); }
     void shrink_to_fit() { squeeze(); }
-    static qsizetype max_size() noexcept
+    static constexpr qsizetype max_size() noexcept
     {
         return Data::max_size();
     }