user32/tests: Make test_WS_VSCROLL() static.

dlls/user32/tests/combo.c

@@ -806,7 +806,7 @@ static void test_listbox_size(DWORD style)
     }
 }
 
-void test_WS_VSCROLL(void)
+static void test_WS_VSCROLL(void)
 {
     BOOL (WINAPI *pGetComboBoxInfo)(HWND, PCOMBOBOXINFO);
     HWND hCombo, hList;