force autotest script to exit with code 1 if any models failed.

[davemfish]

I'm pretty sure this should do the job. An Actions run command that exits with exit 1 should register as a failed step.

Fixes #1468

Checklist

• Updated HISTORY.rst and link to any relevant issue (if these changes are user-facing)
• Updated the user's guide (if needed)
• Tested the Workbench UI (if relevant)

[dcdenu4]

Thanks Dave!