Update lograge/patcher.rb so that the correct logger is checked

[esposito]

What does this PR do?
In this PR I make sure that when the Lograge logger is present, it is checked instead of the Rails logger for showing a warning about tagged logging.

Motivation:
When the lograge keep_original_rails_log option is used, the lograge logger cannot be found in ::Lograge::LogSubscribers::ActionController, as the existing actioncontroller log subscriber is never removed. Therefore the warning in lograge/patcher.rb is shown even when lograge does use a plain logger.

Change log entry
Hide the warning about tagged logging when Lograge uses a plain logger and keep_original_rails_log is enabled.

Additional Notes:

How to test the change?
The change should be covered by the tests. If you want to test it manually, enable the Lograge keep_original_rails_log config option, keep the default Rails logger but use a plain logger in the lograge config. Now there should no longer be an error about tagged logging.