[red-knot] Autoformat mdtest Python snippets using blacken-docs (#13809)

crates/red_knot_python_semantic/resources/mdtest/subscript/instance.md

@@ -3,7 +3,9 @@
 ## Getitem unbound
 
 ```py
-class NotSubscriptable: pass
+class NotSubscriptable: ...
+
+
 a = NotSubscriptable()[0]  # error: "Cannot subscript object of type `NotSubscriptable` with no `__getitem__` method"
 ```
 
@@ -13,6 +15,7 @@ a = NotSubscriptable()[0]  # error: "Cannot subscript object of type `NotSubscri
 class NotSubscriptable:
     __getitem__ = None
 
+
 a = NotSubscriptable()[0]  # error: "Method `__getitem__` of type `None` is not callable on object of type `NotSubscriptable`"
 ```
 
@@ -23,6 +26,7 @@ class Identity:
     def __getitem__(self, index: int) -> int:
         return index
 
+
 reveal_type(Identity()[0])  # revealed: int
 ```
 
@@ -31,13 +35,18 @@ reveal_type(Identity()[0])  # revealed: int
 ```py
 flag = True
 
+
 class Identity:
     if flag:
+
         def __getitem__(self, index: int) -> int:
             return index
+
     else:
+
         def __getitem__(self, index: int) -> str:
             return str(index)
 
+
 reveal_type(Identity()[0])  # revealed: int | str
 ```