Fix docstring for GET run/trace/{id} endpoint in tests

[saathviksheerla]

• The new python implementation intentionally returns 404 (HTTPstatus.NOT_FOUND) for run not found and run trace not found as compared PHP API which retuns 412 (PRECONDITION_FAILED)
• But this is not updated in docstrings that are there in #tests/routers/openml/runs_trace_test.py
  https://github.com/saathviksheerla/server-api/blob/c22d71609a14c8ee2320124cf14854c026a30afc/tests/routers/openml/runs_trace_test.py#L34-L55
• update the docstring to reflect the new implementation.