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_autocmd.vim b/src/testdir/test_autocmd.vim
index 7faa455..3893b79 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
Binary files differ