Fix Santa Hats breaking due to map camouflage (#5268)

# About the pull request

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Simple as it can be - the map camouflage was applied on santa helmets
when they don't have camouflage variants

# Explain why it's good for the game
Spirit of holidays and all that

# Testing Photographs and Procedure
Spawn on a camo-enabled map


# Changelog
:cl:
fix: Fix Xmas helmets getting overriden by map camouflage.
/:cl:

---------

Co-authored-by: Drathek <[email protected]>

code/modules/decorators/christmas.dm

@@ -51,6 +51,7 @@
 	helmet.icon_override = 'icons/mob/humans/onmob/head_0.dmi'
 	helmet.flags_inv_hide = HIDEEARS|HIDEALLHAIR
 	helmet.flags_marine_helmet = NO_FLAGS
+	helmet.flags_atom |= NO_SNOW_TYPE|NO_NAME_OVERRIDE
 	if(prob(50))
 		helmet.icon_state = "santa_hat_red"
 	else