Really fix using sibling wxOwnerDrawnComboBox in wxStaticBoxSizer

This wasn't fixed by 61c28b35e1 (Apply workaround to all sibling
children, not just the first one, 2023-02-20) because the change to
calling MSWDisableComposited() on the window itself, rather than the
static box, was accidentally omitted from it.

src/common/sizer.cpp

@@ -2824,7 +2824,7 @@ bool wxStaticBoxSizer::CheckIfNonBoxChild(wxWindow* win) const
     // box, but it might break the existing code and as we only allow
     // this for compatibility in the first place, it seems better not
     // to risk it.
-    m_staticBox->MSWDisableComposited();
+    win->MSWDisableComposited();
 #endif // __WXMSW__
 
     return true;