executor: fix the case where the job target is set in the job

Fix a case where we pass on a job.py Target rather than a dut.py Target to the executor... which led to a pydantic complaining loudly about it!

On the user side, the issue was seen as the following in the job logs:

ERROR: Could not queue the work: "None"

Fixes: 672a86b3 ("executor/JobRequest: switch to a dataclass") Fixes: #109 (closed)