patch 8.2.4846: termcodes test fails

Problem:    Termcodes test fails.
Solution:   use CTRL-SHIFT-V to insert an unsimplified key. (closes #10316)
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 96723b6..993954b 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -1560,8 +1560,8 @@
   bw!
 endfunc
 
-func Test_gui_CTRL_V()
-  call feedkeys(":let g:str = '\<C-V>\<*C-S-I>\<C-V>\<*C-S-@>'\<CR>", 'tx')
+func Test_gui_CTRL_SHIFT_V()
+  call feedkeys(":let g:str = '\<*C-S-V>\<*C-S-I>\<*C-S-V>\<*C-S-@>'\<CR>", 'tx')
   call assert_equal('<C-S-I><C-S-@>', g:str)
   unlet g:str
 endfunc