Make it compile against qt6

CMakeLists.txt

 project(plymouthkcm)
 
 cmake_minimum_required(VERSION 3.16)
-set(KF5_MIN_VERSION "5.86")
+set(KF5_MIN_VERSION "5.90")
 set(KDE_COMPILERSETTINGS_LEVEL "5.82")
 set(QT_MIN_VERSION "5.15.0")
 
@@ -29,7 +29,7 @@ include(KDECompilerSettings NO_POLICY_SCOPE)
 include(KDEClangFormat)
 include(KDEGitCommitHooks)
 
-find_package(Qt5 ${QT_MIN_VERSION} REQUIRED NO_MODULE COMPONENTS Core Quick Test Gui)
+find_package(Qt${QT_MAJOR_VERSION} ${QT_MIN_VERSION} REQUIRED NO_MODULE COMPONENTS Core Quick Test Gui)
 
 find_package(KF5 ${KF5_MIN_VERSION} REQUIRED COMPONENTS
                     Archive NewStuff NewStuffCore KIO Declarative I18n Config)

src/kcm.cpp

@@ -21,7 +21,6 @@
 #include <QQmlEngine>
 #include <QQuickItem>
 #include <QQuickWindow>
-#include <QStandardItemModel>
 
 #include <KLocalizedString>
 

src/kcm.h

@@ -11,6 +11,7 @@
 
 #include <KNewStuff3/KNSCore/EntryWrapper>
 #include <QDir>
+#include <QStandardItemModel>
 
 #include <KQuickAddons/ConfigModule>