patch 9.0.0232: test with BufNewFile autocmd is flaky

Problem:    Test with BufNewFile autocmd is flaky.
Solution:   Use another file name.
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 5484ecb..b9d8adb 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -1025,23 +1025,23 @@
 
 def Test_bar_line_continuation()
   var lines =<< trim END
-      au BufNewFile Xfile g:readFile = 1
+      au BufNewFile XveryNewFile g:readFile = 1
           | g:readExtra = 2
       g:readFile = 0
       g:readExtra = 0
-      edit Xfile
+      edit XveryNewFile
       assert_equal(1, g:readFile)
       assert_equal(2, g:readExtra)
       bwipe!
       au! BufNewFile
 
-      au BufNewFile Xfile g:readFile = 1
+      au BufNewFile XveryNewFile g:readFile = 1
           | g:readExtra = 2
           | g:readMore = 3
       g:readFile = 0
       g:readExtra = 0
       g:readMore = 0
-      edit Xfile
+      edit XveryNewFile
       assert_equal(1, g:readFile)
       assert_equal(2, g:readExtra)
       assert_equal(3, g:readMore)