vim-patch:partial:8.1.2333: with modifyOtherKeys CTRL-^ doesn't work (#18048)

Problem:    With modifyOtherKeys CTRL-^ doesn't work.
Solution:   Handle the exception.
828ffd5963

test/functional/ui/input_spec.lua

@@ -7,6 +7,7 @@ local curbuf_contents = helpers.curbuf_contents
 local meths = helpers.meths
 local exec_lua = helpers.exec_lua
 local write_file = helpers.write_file
+local funcs = helpers.funcs
 local Screen = require('test.functional.ui.screen')
 
 before_each(clear)
@@ -204,6 +205,13 @@ describe('input pairs', function()
   end)
 end)
 
+it('Ctrl-6 is Ctrl-^ vim-patch:8.1.2333', function()
+  command('split aaa')
+  command('edit bbb')
+  feed('<C-6>')
+  eq('aaa', funcs.bufname())
+end)
+
 describe('input non-printable chars', function()
   after_each(function()
     os.remove('Xtest-overwrite')