Fix flaky rake tests by always loading Rake tasks once

[tdooner]

Ticket

No ticket - flaky tests.

Changes

• Fix flaky rake tests by always loading Rake tasks once

Context for reviewers

If Rails.application.load_tasks is called multiple times, than any
invocation of a Rake task will actually happen multiple times. This is
problematic for non-idempotent Rake tasks (like
users:promote_to_service_account).

Let's prevent this issue by just loading the tasks in the
"rails_helper.rb" file so they're always available.

Acceptance testing

• No acceptance testing needed
  • This change will not affect the user experience (bugfix, dependency updates, etc.)
• Acceptance testing prior to merge
  • This change can be verified visually via screenshots attached below or by sending a link to a local development environment to the acceptance tester
  • Acceptance testing should be done by design for visual changes, product for behavior/logic changes, or both for changes that impact both.
• Acceptance testing after merge
  • This change is hard to test locally, so we'll test it in the demo environment (deployed automatically after merge.)
  • Make sure to notify the team once this PR is merged so we don't inadvertently deploy the unaccepted change to production. (e.g. :alert: Deploy block! @ffs-eng I just merged PR [#123] and will be doing acceptance testing in demo - please don't deploy until I'm finished!)

[allthesignals]

Amazing, thank you! Just tested by duplicating tests in my users spec file.