Allow to build against qt-6.0.

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -204,7 +204,7 @@ endif()
 
 if (ENABLE_QT6)
   SET(QT_NO_CREATE_VERSIONLESS_TARGETS ON)
-  find_package(Qt6 6.2 COMPONENTS Core Gui Widgets Test QUIET)
+  find_package(Qt6 COMPONENTS Core Gui Widgets Test QUIET)
   if (NOT (Qt6Core_FOUND AND Qt6Gui_FOUND AND Qt6Widgets_FOUND AND Qt6Test_FOUND))
     message("-- Package Qt6Core or Qt6Gui or Qt6Widgets or Qt6Test not found")
     set(ENABLE_QT6 OFF)