Adapt to various Qt6 container changes

QHash::unite is gone, container sizes are no longer int, comparison
operators are enforced to be const.

src/kcmkwin/kwinrules/rulebookmodel.cpp

@@ -21,9 +21,8 @@ RuleBookModel::~RuleBookModel()
 
 QHash<int, QByteArray> RuleBookModel::roleNames() const
 {
-    static auto roles = QHash<int, QByteArray> {
-        { DescriptionRole, QByteArray("display") },
-    }.unite(QAbstractListModel::roleNames());
+    auto roles = QAbstractListModel::roleNames();
+    roles.insert(DescriptionRole, QByteArray("display"));
     return roles;
 }
 

src/kcmkwin/kwintabbox/layoutpreview.h

@@ -63,7 +63,7 @@ private:
         QString caption;
         QString icon;
 
-        bool operator==(const ThumbnailInfo &other) {
+        bool operator==(const ThumbnailInfo &other) const {
             return wId == other.wId;
         }
     };

src/x11syncmanager.cpp

@@ -184,7 +184,7 @@ bool X11SyncManager::endFrame()
         return true;
     }
 
-    for (int i = 0; i < std::min(2, m_fences.count() - 1); i++) {
+    for (int i = 0; i < std::min<int>(2, m_fences.count() - 1); i++) {
         const int index = (m_next + i) % m_fences.count();
         X11SyncObject *fence = m_fences[index];