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.
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index a447ba3..d2b9f37 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -289,6 +289,7 @@
 func Test_map_timeout_with_timer_interrupt()
   CheckFeature job
   CheckFeature timers
+  let g:test_is_flaky = 1
 
   " Confirm the timer invoked in exit_cb of the job doesn't disturb mapped key
   " sequence.
@@ -1155,7 +1156,7 @@
   call feedkeys("v\<F4>", 'xt!')
   call assert_equal(['v', 1, 12], [mode(1), col('v'), col('.')])
 
-  " can invoke an opeartor, ending the visual mode
+  " can invoke an operator, ending the visual mode
   let @a = ''
   call feedkeys("\<F5>", 'xt!')
   call assert_equal('n', mode(1))