DevOps: Add unit testing step to the pr_checks workflow

[zackdreitzler]

Describe the task

Add a unit testing check to any PR impacting the frontend code. This check ensures that new JavaScript code is passing all unit tests.

Acceptance Criteria

• A unit test checking step exists on the pr_checks workflow
• When no issues are found, report a success to the PR that triggered this action
• When one or more issues are found, report a failure to the PR that triggered this action

Additional context

This story is also blocked pending a decision on what NextJS unit test suite to use.