Fix deprecation warning when importing from jsonschema (#368)

* Fix deprecation warning when importing from jsonschema

* lint

---------

Co-authored-by: Steven Silvester <steven.silvester@ieee.org>

Author: eladkal

nbformat/json_compat.py

@@ -11,7 +11,7 @@
 import jsonschema
 from fastjsonschema import JsonSchemaException as _JsonSchemaException
 from jsonschema import Draft4Validator as _JsonSchemaValidator
-from jsonschema import ErrorTree, ValidationError
+from jsonschema.exceptions import ErrorTree, ValidationError
 
 
 class JsonSchemaValidator:
@@ -55,7 +55,7 @@ def __init__(self, schema):
     def validate(self, data):
         """Validate incoming data."""
         try:
-            self._validator(data)
+            self._validator(data)  # type:ignore[operator]
         except _JsonSchemaException as error:
             raise ValidationError(str(error), schema_path=error.path) from error
 
@@ -67,7 +67,7 @@ def iter_errors(self, data, schema=None):
         errors = []
         validate_func = self._validator
         try:
-            validate_func(data)
+            validate_func(data)  # type:ignore[operator]
         except _JsonSchemaException as error:
             errors = [ValidationError(str(error), schema_path=error.path)]