Slim down runner tests

[decleaver]

Describe what should be investigated or refactored

The task runner code has been moved out of uds-cli into the maru-runner repo but we have kept the tests to ensure that there are no issues with how maru-runner is being vendored in to uds-cli and being used as a part of uds commands.

We should refactor the uds-cli runner tests to provide the minimum amount of tests such that we still have confidence in the functionality.

The runnerCmd in src/cmd/vendored.go can be used as a starting point for id'ing the logic we want to be covered by these runner tests.