[NFC] Add in Unit test to test domain token replacement in Reply process

[seamuslee001]

Overview

Adds in unit test to test the refactoring Eileen is doing in #24446

Before

No unit test on reply autoresponder

After

We have a unit test (may not be perfect but works at least locally)

ping @eileenmcnaughton

[civibot]

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[eileenmcnaughton]

looks like it needs some teardown

CRM_Mailing_MailingSystemTest::testMailingReplyAutoRespond
Failure in api call for Group create: DB Error: already exists
INSERT INTO civicrm_group (name , title , description , is_active , visibility , group_type ) VALUES ('Test Group 1' , 'New Test Group Created' , 'New Test Group Created' , 1 , 'Public Pages' , '12' ) [nativecode=1062 ** Duplicate entry 'Test Group 1' for key 'UI_name']
#0 /home/jenkins/bknix-dfl/build/core-24453-88bhx/web/sites/all/modules/civicrm/vendor/pear/pear-core-minimal/src/PEAR.php(944): CRM_Core_Error::exceptionHandler(Object(DB_Error))