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_viminfo.vim b/src/testdir/test_viminfo.vim
index c3ec5b0..7101727 100644
--- a/src/testdir/test_viminfo.vim
+++ b/src/testdir/test_viminfo.vim
@@ -722,6 +722,7 @@
 endfunc
 
 func Test_viminfo_oldfiles()
+  set noswapfile
   let v:oldfiles = []
   let lines = [
 	\ '# comment line',
@@ -765,6 +766,7 @@
   call assert_equal("/tmp/another.txt", expand("%"))
   bwipe
   delmark E
+  set swapfile&
 endfunc
 
 " Test for storing and restoring buffer list in 'viminfo'