From the project PM-3810, the goal was to deprecate the rollback reason API and we were not able to due the many-collection test failing. The many-collection test was failing due to rollback_reason() not being removed from the public MongoDB repo because it had not been synced to the private repo.

As a workaround, we have decided for the many-collection test to use a custom branch such that we can go ahead with deprecate the rollback reason API. I have created a follow on ticket to re-enable using the MongoDB master branch once copybara is on again. The steps are as is:

1. Create custom branch on MongoDB branch
2. Cherry-pick the commit that removes the rollback reason API
3. Push the branch to the repo
4. Make evergreen changes to refer to that branch