Replace forum.kde.org with discuss.kde.org

The old forum is deprecated.

src/workspace.cpp

@@ -1833,7 +1833,7 @@ QString Workspace::supportInformation() const
 
     support.append(ki18nc("Introductory text shown in the support information.",
                           "KWin Support Information:\n"
-                          "The following information should be used when requesting support on e.g. https://forum.kde.org.\n"
+                          "The following information should be used when requesting support on e.g. https://discuss.kde.org.\n"
                           "It provides information about the currently running instance, which options are used,\n"
                           "what OpenGL driver and which effects are running.\n"
                           "Please post the information provided underneath this introductory text to a paste bin service\n"