Increase timeout for FetchInternalRemote RPC call

This call is currently only used by `UpdateRepositoryStorageService`,
and it can easily time out after 30 seconds for large projects. Increase
it to a long timeout to ensure this doesn't fail prematurely.

Encountered in
https://gitlab.com/gitlab-com/gl-infra/production/issues/1250

changelogs/unreleased/use-long_timeout-for-fetch_internal_remote_gitaly-rpc.yml

+---
+title: Increase timeout for FetchInternalRemote RPC call
+merge_request: 18908
+author:
+type: fixed

lib/gitlab/gitaly_client/remote_service.rb

@@ -49,7 +49,7 @@ module Gitlab
 
         response = GitalyClient.call(@storage, :remote_service,
                                      :fetch_internal_remote, request,
-                                     timeout: GitalyClient.medium_timeout,
+                                     timeout: GitalyClient.long_timeout,
                                      remote_storage: repository.storage)
 
         response.result