Review getDefaultTagId()

Problem/Motivation

getDefaultTagId() appears that it should be checking for the first GTM code in the list to match GOOGLE_TAG_MANAGER_MATCH regex. However, the condition is === 0 meaning that it will return the first code that doesn't match the regex of GOOGLE_TAG_MANAGER_MATCH

I believe the condition should be === 1 and the first code in tests should be 'GTM-XXXXXX' instead of 'GT-XXXXXX'

Steps to reproduce

Change the unit test to 'GTM-XXXXXX' in PageAttachmentsHookTest::testAttachments and see it fail.

Proposed resolution

Change the condition and update the tests to use the correct code.

Remaining tasks

Review the incoming merge request