Debugger: Add missing stretch

Amends 2b97f69796.

Change-Id: I44ddf368990c7ebbeeb5c07569ac5811a56f3c10
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/gdb/gdboptionspage.cpp

@@ -55,7 +55,8 @@ public:
                     s.intelFlavor,
                     s.usePseudoTracepoints,
                     s.useIndexCache,
-                 }
+                    st
+                }
             };
 
             Group extended {