Fix build with Qt 6

We don't need any of the OpenGL-specific link handling there.

libtaskmanager/declarative/CMakeLists.txt

@@ -35,13 +35,15 @@ target_link_libraries(taskmanagerplugin Qt::Qml Qt::GuiPrivate
                                         KF5::I18n
                                         Qt::WaylandClient
                                         Wayland::Client)
-if (${Qt5Gui_OPENGL_IMPLEMENTATION} STREQUAL "GLESv2")
-    target_link_libraries(taskmanagerplugin Qt5::Gui_GLESv2)
-elseif(TARGET Qt5::Gui_GL)
-    target_link_libraries(taskmanagerplugin Qt5::Gui_GL)
-endif()
-if (TARGET Qt5::Gui_EGL)
-    target_link_libraries(taskmanagerplugin Qt5::Gui_EGL)
+if (QT_MAJOR_VERSION EQUAL "5")
+    if (${Qt5Gui_OPENGL_IMPLEMENTATION} STREQUAL "GLESv2")
+        target_link_libraries(taskmanagerplugin Qt5::Gui_GLESv2)
+    elseif(TARGET Qt5::Gui_GL)
+        target_link_libraries(taskmanagerplugin Qt5::Gui_GL)
+    endif()
+    if (TARGET Qt5::Gui_EGL)
+        target_link_libraries(taskmanagerplugin Qt5::Gui_EGL)
+    endif()
 endif()
 
 if(TARGET K::KPipeWire)