Donator masks now properly protect from cold (#4032)

# About the pull request
As title. All other donor gear has cold protection, just not mask.
Causes inconsistencies/problems on cold maps.
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# Explain why it's good for the game
Consistency is a good thing, usually.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

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# Changelog
:cl:
fix: Donator custom masks now properly protect from cold weather.
/:cl:

code/modules/cm_marines/Donator_Items.dm

@@ -55,6 +55,8 @@
 	//DON'T GRAB STUFF BETWEEN THIS LINE
 	flags_inventory = ALLOWREBREATH
 	flags_inv_hide = HIDEEARS|HIDEEYES|HIDEFACE
+	flags_cold_protection = BODY_FLAG_HEAD
+	min_cold_protection_temperature = ICE_PLANET_MIN_COLD_PROT
 	//AND THIS LINE
 
 //END MASK TEMPLATE