patch 9.0.0415: on MS-Windows some tests are flaky

Problem:    On MS-Windows some tests are flaky.
Solution:   Add sleeps, disable swapfile, mark test as flaky. (Ken Takata,
            closes #11082)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 669089d..3370190 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -763,6 +763,7 @@
 
   call writefile(content, 'Xvimrc', 'D')
   call system(GetVimCommand('Xvimrc') .. ' --not-a-term --noplugins -S Session.vim -c cq')
+  sleep 50m
   let errors = join(readfile('Xerrors'))
   call assert_match('E814:', errors)