partial: Replace returns plugin with an annotation.

The returns plugin hasn’t been updated for mypy ≥ 1.6.  This
annotation is more limited in that it only supports a fixed number of
positional arguments and no keyword arguments, but is good enough for
our purposes.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/webhooks/github/view.py

@@ -3,10 +3,10 @@ from datetime import datetime, timezone
 from typing import Callable, Dict, Optional
 
 from django.http import HttpRequest, HttpResponse
-from returns.curry import partial
 
 from zerver.decorator import log_unsupported_webhook_event, webhook_view
 from zerver.lib.exceptions import UnsupportedWebhookEventTypeError
+from zerver.lib.partial import partial
 from zerver.lib.response import json_success
 from zerver.lib.typed_endpoint import JsonBodyPayload, typed_endpoint
 from zerver.lib.validator import WildValue, check_bool, check_int, check_none_or, check_string