Fixes and includes clothing_under_armor_subtype_check.dm in the unit tests. (#76351)

## About The Pull Request
See #76345 (which said:

Unit test clothing_under_armor_subtype_check is unticked in _unit_test.dm and also would fail if it was ticked

It's not included, it doesn't run

Even if it would run, it's currently doing an istype when it should be doing an ispath, so it'd fail)

## Why It's Good For The Game
This will fix #76345.

## Changelog
N/A

code/modules/unit_tests/_unit_tests.dm

@@ -103,6 +103,7 @@
 #include "chat_filter.dm"
 #include "circuit_component_category.dm"
 #include "closets.dm"
+#include "clothing_under_armor_subtype_check.dm"
 #include "combat.dm"
 #include "component_tests.dm"
 #include "confusion.dm"

code/modules/unit_tests/clothing_under_armor_subtype_check.dm

@@ -5,4 +5,5 @@
 
 /datum/unit_test/clothing_under_armor_subtype_check/Run()
 	for(var/obj/item/clothing/under/jumpsuit as anything in typesof(/obj/item/clothing/under))
-		TEST_ASSERT(istype(initial(jumpsuit.armor_type), /datum/armor/clothing_under), "[initial(jumpsuit.type)] does not use clothing_under as its armor!")
+		if(!ispath(initial(UNLINT(jumpsuit.armor_type)), /datum/armor/clothing_under))
+			TEST_FAIL("[jumpsuit] does not use clothing_under as its armor!")