patch 9.2.0810: add_llist_tags() uses wrong function to free dict

patch 9.2.0810: add_llist_tags() uses wrong function to free dict

Problem:  add_llist_tags() uses wrong function to free dict on alloc
          failure
Solution: Use dict_unref() (Yasuhiro Matsumoto).

add_llist_tags() released a dict_alloc()'d dict with vim_free() when
list_append_dict() failed, leaving a dangling pointer in the dict
garbage-collection chain. Use dict_unref().

related: #20668
closes:  #20743

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>