When Running rspec with --warnings enabled a warning is emitted by the
rollbar gem.

```
$ rspec --warnings
/my/path/ruby-3.2.2/gems/rollbar-3.4.1/lib/rollbar/json.rb:8: warning: attribute accessor as module_function
```

This is caused by the line
```
attr_writer :options_module
```
Within [lib/rollbar/json.rb](https://github.com/rollbar/rollbar-gem/blob/8c6a9e94629c0a8b964f0a3b13eab742c3800841/lib/rollbar/json.rb#L8)

The line was introduced here, when there was a more complicated way of configuring the json parser.

e33f10e#diff-9e64389290ff8e4e50cba9436521333bdd3307baa63ed84b74f0f9b28a6cfceaR13

However in 2019 this code was removed, and replaced with Ruby's JSON module

de45e80#diff-9e64389290ff8e4e50cba9436521333bdd3307baa63ed84b74f0f9b28a6cfceaL39-L41

But the attr_writer was (accidentally?) not removed.

As the `options_module` attribute writer is not documented or referenced anywhere else in the project I believe it can be removed.

This commit removes the unused `attr_writer` and fixes the warning.

Fixes: #1108

When enabled, this adds job data to any Rollbar reporting that happens
within the job, and prevents changes to the scope from polluting the
global scope for other jobs.

Co-authored-by: Walt Jones <[email protected]>

)

* make ActiveJob plugin a true plugin, with disable

* add rescue_from to ActionMailer::Base, not MailDeliveryJob

* test for Rails 6+ first. (DeliveryJob is always defined.)

* limit DeliveryJob tests to Rails < 6.x

* update test app config for rails 6+

* handle undefined job_id

* refactor to test both DeliveryJob and MailDeliveryJob

* allow both hash syntaxes

* enable Rails 7 error reporter via Rollbar config

* initialize logger base class

* use Logger version

* apply capture_uncaught config to rails error subscriber