Validate datetimes in metadata

[mhpob]

When validating a metadata file using this GitHub Action, datetimes such as "2024-03-26T14:00:00Z" error with "can't compare offset-naive and offset-aware datetimes". This does not happen for me locally when using yamale -s <schema> -p ruamel <file>, but does happen when using the default -p PyYAML (yamale -s <schema> <file>).

Example error:
https://github.com/ocean-tracking-network/demo-data/actions/runs/8430264168/job/23085844309#step:5:7

I've submitted a PR to validate deployment/recovery datetime as strings to get past the check, but I think we would want to validate them as datetimes. Not sure what I'm missing between my system and the blank runner used by GitHub.