Adds holiday mail to Christmas season (#94558)

## About The Pull Request

- Now that the Christmas holiday is extended to ~2 weeks, re-enables
mail for the duration of the holiday.
- Adds some Christmas specific goodies to add to the mail pool for the
duration.

## Why It's Good For The Game

2 weeks without any mail is a rather long time. Also what about all that
Christmas space cash you receive from relatives who you never visit?

## Changelog

🆑 LT3
add: Christmas season now includes Christmas themed goodies in the mail
/🆑

code/modules/holiday/holidays.dm

@@ -847,7 +847,13 @@ GLOBAL_LIST_INIT(holiday_mail, list())
 	begin_month = DECEMBER
 	end_day = 27
 	holiday_hat = /obj/item/clothing/head/costume/santa
-	no_mail_holiday = TRUE
+	holiday_mail = list(
+		/obj/item/clothing/head/beanie/christmas,
+		/obj/item/clothing/neck/scarf/christmas,
+		/obj/item/food/cookie/sugar,
+		/obj/item/gift/anything,
+		/obj/item/toy/xmas_cracker,
+	)
 	holiday_colors = list(
 		COLOR_CHRISTMAS_GREEN,
 		COLOR_CHRISTMAS_RED,