vim-patch:8.2.3518: Test_xrestore sometimes fails

Problem:    Test_xrestore sometimes fails.
Solution:   Mark the test as flayky.  Move marking test as flaky to the test
            instead of listing them in runtest.

f08b0eb869

Co-authored-by: Bram Moolenaar <Bram@vim.org>

test/old/testdir/test_functions.vim

@@ -2567,6 +2567,7 @@ endfunc
 
 func Test_state()
   CheckRunVimInTerminal
+  let g:test_is_flaky = 1
 
   let getstate = ":echo 'state: ' .. g:state .. '; mode: ' .. g:mode\<CR>"