Provide changes that fix tests for Rails 6.1

What does this MR do?

Rails 6.1 update !59107 (merged) required some small changes in order to fix the breaking changes it introduces.

It seems like an overhead to create separate merge requests for each of them since they are small. But each of them may raise a discussion, so extracting them in a separate merge request should make the review easier.

This MR consists of 8 commits with their own commits messages with an explanation why a particular change is introduced, so it'll be more convenient to review this MR commit-by-commit.