Why Can't I Add Work Items of the Task Type When a Test Plan Is Created or Updated?

Symptom

In a Scrum project, work items of the Task type cannot be selected when adding a requirement to the test plan.

Root Cause

In a Scrum project, the Task type is more oriented towards a specific development task than a complete requirement story.

Therefore, only the Epic, Feature, and Story work items of a Scrum project can be added to the test plan. Work items of the Task and other custom types cannot be added to the test plan.