I have completed some work on Case Manager that's ready for review!
This pull request makes the following changes:

1) Set action_dispatch.show_exceptions to :none

The deprecation warning:
Setting action_dispatch.show_exceptions to false is deprecated. Set to :none instead. (called from block (4 levels) in class:LinesControllerTest at /home/runner/work/dcaf_case_management/dcaf_case_management/test/controllers/lines_controller_test.rb:34)
is due to a change in how Rails handles the action_dispatch.show_exceptions configuration setting.
Setting it to :none will have the same effect as setting it to false in the previous version.

2) Conditional Secret Key Assignment for Test Environment

The secret key for Devise is now explicitly set to Rails.application.secret_key_base in test environments .
This is a temporary workaround for the tests deprecation warning: Rails.application.secrets is deprecated in favor of Rails.application.credentials and will be removed in Rails 7.2. See related issue.

Next Steps

As part of Rails' evolution, accessing secrets via Rails.application.secrets is being deprecated in favor of Rails.application.credentials. This change aims to enhance security and streamline secret management by utilizing encrypted credentials.
I would consider migrating all sensitive credentials from the unencrypted secrets.yml file to Rails' encrypted credentials system (credentials.yml.enc). I can do this on this PR and share the necessary master key securely via SendSafely with a team member who has the requisite Heroku access. This will allow us to set up the environment variables on Heroku securely and complete the migration process.

It relates to the following issue #s:

• Fixes Rails deprecation warnings #3128

For reviewer:

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