yaml linter fix & alert sprite specifier changes (#10015)

* Sprite specifier/serializer update

* Immume

* Fix tests

* hooray, more bad test prototypes

* add some comments

Resources/Prototypes/Entities/Mobs/Customization/Markings/cat_parts.yml

@@ -4,9 +4,9 @@
   markingCategory: HeadTop
   speciesRestriction: [Human]
   sprites:
-  - sprite: Mobs/Customization/cat_parts.rsi/
+  - sprite: Mobs/Customization/cat_parts.rsi
     state: ears_cat_outer
-  - sprite: Mobs/Customization/cat_parts.rsi/
+  - sprite: Mobs/Customization/cat_parts.rsi
     state: ears_cat_inner
 
 - type: marking
@@ -15,5 +15,5 @@
   markingCategory: Tail
   speciesRestriction: [Human]
   sprites:
-  - sprite: Mobs/Customization/cat_parts.rsi/
+  - sprite: Mobs/Customization/cat_parts.rsi
     state: tail_cat