LoW S09 Lua cleanup: fix a line that was missed in 3783693 (#2835)

3783693 was a general rename of
'V' to 'vars', and this line was missed. It caused an error at the
start of S09.

[ci skip]

data/campaigns/Legend_of_Wesmere/lua/wml_tags.lua

@@ -94,7 +94,7 @@ function wesnoth.wml_actions.persistent_carryover_store(cfg)
 end
 
 function wesnoth.wml_actions.persistent_carryover_unstore(cfg)
-	if V.side_number then
+	if vars.side_number then
 		-- Only do this if we begin from this chapter.
 		return
 	end