ref: unify signature of get_release_hook (#74897)

fixes errors pointed out by upgrading mypy to 1.11

<!-- Describe your PR here. -->

src/sentry/plugins/base/v2.py

@@ -11,6 +11,7 @@
 from sentry.plugins.base.configuration import default_plugin_config, default_plugin_options
 from sentry.plugins.base.response import Response
 from sentry.plugins.config import PluginConfigMixin
+from sentry.plugins.interfaces.releasehook import ReleaseHook
 from sentry.plugins.status import PluginStatusMixin
 from sentry.utils.hashlib import md5_text
 
@@ -411,7 +412,7 @@ def get_feature_hooks(self, **kwargs):
         """
         return []
 
-    def get_release_hook(self, **kwargs):
+    def get_release_hook(self) -> type[ReleaseHook] | None:
         """
         Return an implementation of ``ReleaseHook``.
 
@@ -421,10 +422,10 @@ def get_release_hook(self, **kwargs):
         >>>     def handle(self, request: Request) -> Response:
         >>>         self.finish_release(version=request.POST['version'])
 
-        >>> def get_release_hook(self, **kwargs):
+        >>> def get_release_hook(self):
         >>>     return MyReleaseHook
         """
-        return []
+        return None
 
     def get_custom_contexts(self):
         """Return a list of of context types.

src/sentry_plugins/heroku/plugin.py

@@ -215,5 +215,5 @@ def get_release_doc_html(self, hook_url):
         <pre class="clippy">heroku webhooks:add -i api:release -l notify -u {hook_url} -a YOUR_APP_NAME</pre>
         """
 
-    def get_release_hook(self):
+    def get_release_hook(self) -> type[HerokuReleaseHook]:
         return HerokuReleaseHook