patch 8.2.1658: expand('<stack>') has trailing ".."

Problem:    Expand('<stack>') has trailing "..".
Solution:   Remove the "..". (closes #6927)
diff --git a/src/testdir/test_expand_func.vim b/src/testdir/test_expand_func.vim
index a63cc04..3c430e1 100644
--- a/src/testdir/test_expand_func.vim
+++ b/src/testdir/test_expand_func.vim
@@ -58,7 +58,7 @@
   END
   call writefile(lines, 'Xstack')
   source Xstack
-  call assert_match('\<Xstack\[2\]', g:stack_value)
+  call assert_match('\<Xstack\[2\]$', g:stack_value)
   call delete('Xstack')
 endfunc