`SendReplyJob` was caching reloadable service class objects in
`CHANNEL_SERVICES`. In test, a request spec can trigger Rails constant
reloading after `SendReplyJob` has already been loaded, leaving the job
with stale class objects while later specs stub the reloaded constants.
This resolves the channel service at perform time so the job follows the
current Rails constant table.
How to reproduce
Run the CircleCI shard that contains send_reply_job_spec, or the
minimized order-dependent reproduction:
```sh
bundle exec rspec --format progress spec/builders/v2/reports/label_summary_builder_spec.rb spec/controllers/api/v1/accounts/bulk_actions_controller_spec.rb spec/jobs/send_reply_job_spec.rb:32
```
What changed
- Store service class names in `SendReplyJob::CHANNEL_SERVICES` instead
of class objects.
- Resolve the service with constantize inside perform so reloads do not
leave stale cached classes.
Co-authored-by: Sony Mathew <2040199+sony-mathew@users.noreply.github.com>
