Use wxID_HIGHEST instead of wxID_HIGHEST+1 in samples

There is no need to add 1 any more since the changes of 99c52403f9 (Use
usual half-open interval for wxID_LOWEST..wxID_HIGHEST, 2022-10-23), so
don't.

Closes #22923.

samples/vscroll/vstest.cpp

@@ -431,7 +431,7 @@ enum
     // (where it is special and put into the "Apple" menu)
     VScroll_About = wxID_ABOUT,
 
-    VScroll_VScrollMode = wxID_HIGHEST + 1,
+    VScroll_VScrollMode = wxID_HIGHEST,
     VScroll_HScrollMode,
     VScroll_HVScrollMode
 };