vim-patch:8.0.0338: :recover test fails on MS-Windows

Problem:    :recover test fails on MS-Windows.
Solution:   Use non-existing directory on MS-Windows.

803452046b

src/nvim/testdir/test_recover.vim

@@ -7,6 +7,10 @@ func Test_recover_root_dir()
   call assert_fails('recover', 'E305:')
   close!
 
+  if has('win32')
+    " can write in / directory on MS-Windows
+    set dir=/notexist/
+  endif
   call assert_fails('split Xtest', 'E303:')
   set dir&
 endfunc