vim-patch:9.0.0216: undo earlier test sometimes fails on MS-Windows (#19790)

Problem:    Undo earlier test sometimes fails on MS-Windows.
Solution:   Use another file name.
cce293f87b

src/nvim/testdir/test_undo.vim

@@ -336,7 +336,7 @@ func Test_undofile_earlier()
   " create undofile with timestamps older than Vim startup time.
   let t0 = localtime() - 43200
   call test_settime(t0)
-  new Xfile
+  new XfileEarlier
   call feedkeys("ione\<Esc>", 'xt')
   set ul=100
   call test_settime(t0 + 1)
@@ -350,12 +350,12 @@ func Test_undofile_earlier()
   bwipe!
   " restore normal timestamps.
   call test_settime(0)
-  new Xfile
+  new XfileEarlier
   rundo Xundofile
   earlier 1d
   call assert_equal('', getline(1))
   bwipe!
-  call delete('Xfile')
+  call delete('XfileEarlier')
   call delete('Xundofile')
 endfunc