kitchen_sink.grpahql: add @onVariableDefinition directive

Replicates graphql/graphql-js@1a96306

Author: Cito

tests/fixtures/kitchen_sink.graphql

@@ -28,7 +28,7 @@ mutation likeStory @onMutation {
 }
 
 subscription StoryLikeSubscription(
-  $input: StoryLikeSubscribeInput
+  $input: StoryLikeSubscribeInput @onVariableDefinition
 ) @onSubscription {
   storyLikeSubscribe(input: $input) {
     story {

tests/language/test_printer.py

@@ -168,7 +168,7 @@ def prints_kitchen_sink_without_altering_ast(kitchen_sink_query):  # noqa: F811
               }
             }
 
-            subscription StoryLikeSubscription($input: StoryLikeSubscribeInput) @onSubscription {
+            subscription StoryLikeSubscription($input: StoryLikeSubscribeInput @onVariableDefinition) @onSubscription {
               storyLikeSubscribe(input: $input) {
                 story {
                   likers {

tests/language/test_visitor.py

@@ -897,6 +897,10 @@ def leave(*args):
             ["enter", "name", "name", "named_type"],
             ["leave", "name", "name", "named_type"],
             ["leave", "named_type", "type", "variable_definition"],
+            ["enter", "directive", 0, None],
+            ["enter", "name", "name", "directive"],
+            ["leave", "name", "name", "directive"],
+            ["leave", "directive", 0, None],
             ["leave", "variable_definition", 0, None],
             ["enter", "directive", 0, None],
             ["enter", "name", "name", "directive"],