The settings form is missing test coverage

Problem/Motivation

As part of 📌 Fix coding standard | PHPCS Active it was discovered that test coverage is missing for the Settings form causing the form to fail with WSOD after the site is upgraded to D11. The root cause for this was a new dependency being added to ConfigFormBase class. Due to a lack of test coverage the problem was not uncovered by Gitlab CI

Proposed resolution

Add test coverage to check if the form loads, and can be submitted successfully.