fix: track error results seen in sim flows

With errors in sim flows, we were not getting an error log or the
correct erroneous exit code because the "errors_seen" state variable of
the SimCfg was not being updated correctly.

Signed-off-by: Alex Jones <alex.jones@lowrisc.org>

Author: AlexJones0

src/dvsim/sim/flow.py

@@ -795,6 +795,8 @@ def make_test_result(tr) -> TestResult | None:
         )
 
         failures = BucketedFailures.from_job_status(results=run_results)
+        if failures.buckets:
+            self.errors_seen = True
 
         # --- Final result ---
         return SimFlowResults(