Fixing create_runtime unit test.

[tim-shea]

Issue

Issue Number: #717

Objective

Objective of pull request: Fixing create_runtime unit test.

Pull request checklist

Your PR fulfills the following requirements:

• [X] Issue created that explains the change and why it's needed
• [X] Tests are part of the PR (for bug fixes / features)
• [X] Docs reviewed and added / updated if needed (for bug fixes / features)
• [X] PR conforms to Coding Conventions
• [X] PR applys BSD 3-clause or LGPL2.1+ Licenses to all code files
• [X] Lint (flakeheaven lint src/lava tests/) and (bandit -r src/lava/.) pass locally
• [X] Build tests (pytest) passes locally

Pull request type

• [X] Bugfix

What is the current behavior?

• The unit test is failing due to an unimplemented method in a Mock object.

What is the new behavior?

• The unit test is passing.

Does this introduce a breaking change?

• [X] No