Test: Add tests for form migration steps

[pauloiankoski]

Resolves GIVE-803

Description

This PR adds a helper method to be used when testing FormMIgration processes and updates the existing tests to use that helper.

Additionally, after reviewing them, I've found a bug with the ConvertKit process that required a fix: the conditional logic for canHandle was not correct when the selected option on v2 was to customize per form.

Affects

Form Migration tests

Testing Instructions

The only test to do here is regarding the ConvertKit issue I've found so:

1. Using the current version of Give core, configure a v2 form with customized ConvertKit settings while not enabling it globally
2. Migrate that form
3. Confirm that ConvertKit settings have not been migrated correctly
4. Upgrade Give to this version
5. Repeat the process
6. ConvertKit settings must have been migrated as expected now

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[github-actions]

This PR is stale because it has been open 45 days with no activity. Stale PRs will NOT be automatically closed.

[jonwaldstein]

Great job!

[rickalday]

Passed manual QA tests.