Fix: Form Builder: Tag and add to Sequence when adding to Form fails

[n7studios]

Summary

Fixes the Form Builder block not tagging the subscriber or adding them to the Sequence when adding the subscriber to the Form failed.

After creating the subscriber, $result was overwritten by the add to Form request. The Tag and Sequence requests then read the subscriber ID from $result['subscriber']['id']. If the Form request failed, $result was a WP_Error, so the subscriber ID was missing and the Tag and Sequence requests failed.

The subscriber ID is now stored once, after the subscriber is created, and used for the Form, Tag and Sequence requests.

Testing

New Integration test in BlockFormBuilderTest:

• testTagAndSequenceWhenAddingSubscriberToFormFails: mocks the add to Form request returning an error, and confirms the subscriber is still tagged and added to the Sequence. Fails without this fix.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)