fix typo in docs

Author: aryaniyaps

docs/execution/validation.rst

@@ -20,7 +20,7 @@ Example
 Here is how you would implement depth-limiting on your schema.
 
 .. code:: python
-    from graphql import validate
+    from graphql import validate, parse
     from graphene import ObjectType, Schema, String
     from graphene.validation import depth_limit_validator
 
@@ -36,7 +36,7 @@ Here is how you would implement depth-limiting on your schema.
 
     validation_errors = validate(
         schema=schema,
-        document='THE QUERY',
+        document_ast=parse('THE QUERY'),
         rules=(
             depth_limit_validator(
                 max_depth=20

graphene/validation/tests/test_depth_limit_validator.py

@@ -87,8 +87,8 @@ def callback(query_depths):
         result = query_depths
 
     errors = validate(
-        schema.graphql_schema,
-        document,
+        schema=schema.graphql_schema,
+        document_ast=document,
         rules=(
             depth_limit_validator(
                 max_depth=max_depth,

graphene/validation/tests/test_disable_introspection.py

@@ -19,8 +19,8 @@ def run_query(query: str):
     result = None
 
     errors = validate(
-        schema.graphql_schema,
-        document,
+        schema=schema.graphql_schema,
+        document_ast=document,
         rules=(
             disable_introspection(),
         ),