QDuplicateTracker: port reserve() from int to qsizetype

Was missed in the int -> qsizetype port for Qt 6.0.

Change-Id: I1ae8190601f2e1a1bc02a736c12230a9c71acb18
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit fcfc854def12500658d5d863797169279b698498)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/tools/qduplicatetracker_p.h

@@ -89,7 +89,7 @@ class QDuplicateTracker {
     Q_DISABLE_COPY_MOVE(QDuplicateTracker);
 public:
     QDuplicateTracker() = default;
-    void reserve(int n) { set.reserve(n); }
+    void reserve(qsizetype n) { set.reserve(n); }
     [[nodiscard]] bool hasSeen(const T &s)
     {
         bool inserted;