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.

src/testdir/test_functions.vim

@@ -2286,6 +2286,7 @@ endfunc
 
 func Test_state()
   CheckRunVimInTerminal
+  let g:test_is_flaky = 1
 
   let getstate = ":echo 'state: ' .. g:state .. '; mode: ' .. g:mode\<CR>"