Fix logic error in DBus script evaluation

Was mentioned in review, yet somehow slipped through

shell/shellcorona.cpp

@@ -1465,7 +1465,7 @@ void ShellCorona::loadKWinScriptInInteractiveConsole(const QString &script)
 }
 
 void ShellCorona::evaluateScript(const QString &script) {
-    if (immutability() != Plasma::Types::SystemImmutable) {
+    if (immutability() == Plasma::Types::SystemImmutable) {
         if (calledFromDBus()) {
             sendErrorReply(QDBusError::Failed, QStringLiteral("Widgets are locked"));
         }