Update scrontab to prune slurm logs

[blinkdog]

cd /global/homes/i/icecubed/lta/slurm-logs; find . -type f -mtime 7 -delete

Not the most brilliant construction. If /global/homes/i/icecubed/lta/slurm-logs doesn't exist or is somehow inaccessible, it deletes things exactly a week old wherever scrontab jobs happen to start ... is that ${HOME}? No idea.

Replaced with:
find /global/homes/i/icecubed/lta/slurm-logs -type f -mtime +7 -delete

This will find in the provided directory, or fail, and the +7 means we get all the logs one week and older, not just those exactly a week old.

[blinkdog]

This is failing on test setups that want new Python 3.12 dependencies, but...

1. We use Python 3.10 in the deployment on Perlmutter at NERSC.
2. This PR is not a code change; it captures a configuration change already made at NERSC.

I'll merge this one and hope for better 3.12 support in CI/CD the future.