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_terminal2.vim b/src/testdir/test_terminal2.vim
index 0f8dcb6..68f9ad8 100644
--- a/src/testdir/test_terminal2.vim
+++ b/src/testdir/test_terminal2.vim
@@ -217,6 +217,7 @@
   CheckUnix
   " TODO: Somehow this test sometimes hangs in the GUI
   CheckNotGui
+  let g:test_is_flaky = 1
 
   " Let the terminal output more than 'termwinscroll' lines, some at the start
   " will be dropped.
@@ -412,6 +413,7 @@
   if has('conpty')
     throw 'Skipped: fail on ConPTY'
   endif
+  let g:test_is_flaky = 1
   let contents = [
   \   [ 'One', '', 'X' ],
   \   [ 'Two', '', '' ],