chore(auth): Add waits to asynchronous tests

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:
I noticed that unit tests in RealAuthCognitoPluginTest were frequently failing on CI. Inspecting the failing tests show that they were not necessarily waiting for the callbacks to be invoked before proceeding with verification. Adding additional latches should resolve the issue.

Longer term this area of the codebase should be refactored into usecases.

How did you test these changes?
(Please add a line here how the changes were tested)

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.