Secbelts can now hold knives. (shiptest-ss13#3455)

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## About The Pull Request
Title.
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## Why It's Good For The Game
A knife is a pretty common piece of sec gear in the frontier actually.
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## Changelog

:cl:
tweak: You can now put knives in secbelts and the subtypes of secbelts.
fix: You can now fit all knives in mining webbings.
/:cl:

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code/game/objects/items/storage/belt.dm

@@ -275,6 +275,7 @@
 	STR.set_holdable(list(
 		/obj/item/melee/baton,
 		/obj/item/melee/classic_baton,
+		/obj/item/melee/knife,
 		/obj/item/grenade,
 		/obj/item/reagent_containers/spray/pepper,
 		/obj/item/restraints/handcuffs,
@@ -367,7 +368,7 @@
 		/obj/item/storage/fancy/cigarettes,
 		/obj/item/reagent_containers/food/drinks/bottle,
 		/obj/item/stack/medical,
-		/obj/item/melee/knife/kitchen,
+		/obj/item/melee/knife,
 		/obj/item/reagent_containers/hypospray,
 		/obj/item/gps,
 		/obj/item/storage/bag/ore,