Require Qt >=6.5 at CMake configure time

This was raised to at least 6.5 in 7660ad0
but this wasn't enforced. And not for lack of trying, the version check
wouldn't have worked as the name of the variable was wrong too.

Author: redstrate

CMakeLists.txt

@@ -437,8 +437,8 @@ endif()
 set_package_properties(Qt${QT_VERSION_MAJOR}Core PROPERTIES TYPE REQUIRED)
 
 find_package(Qt${QT_VERSION_MAJOR} NO_MODULE REQUIRED COMPONENTS Gui Network)
-if(QT_VERSION_MAJOR EQUAL 6 AND QT_VERSION_MINOR LESS 3)
-    message(FATAL_ERROR "Sorry, Qt6 less than version 6.3 is not supported since GammaRay 3.1")
+if(QT_VERSION_MAJOR EQUAL 6 AND Qt${QT_VERSION_MAJOR}Core_VERSION_MINOR LESS 5)
+    message(FATAL_ERROR "Sorry, Qt6 less than version 6.5 is not supported since GammaRay 3.3")
 endif()
 
 find_package(