add hostname to output from app_env_wrapper

[JorgeBornemann]

Fixes #630

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• [ ] Documentation has been updated to reflect change.
• [ ] New code has tests, and affected old tests have been updated.
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[github-actions[bot]]

[JorgeBornemann]

Trivial change to add to the output which machine/node app_env_wrapper is running in. This will help troubleshooting, particularly when the tasks are submitted via slurm/psb, without having to get the job-id and find the running node(s) from there.

[JorgeBornemann]

Closing PR as not required.