patch 9.0.1570: some tests are slow

Problem:    Some tests are slow.
Solution:   Make a few test cases faster.
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index 9bb21bc..79740b5 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -791,10 +791,10 @@
 endfunc
 
 func Test_expand_star_star()
-  call mkdir('a/b', 'pR')
-  call writefile(['asdfasdf'], 'a/b/fileXname')
-  call feedkeys(":find **/fileXname\<Tab>\<CR>", 'xt')
-  call assert_equal('find a/b/fileXname', @:)
+  call mkdir('a/b/c', 'pR')
+  call writefile(['asdfasdf'], 'a/b/c/fileXname')
+  call feedkeys(":find a/**/fileXname\<Tab>\<CR>", 'xt')
+  call assert_equal('find a/b/c/fileXname', @:)
   bwipe!
 endfunc