Convert from groovy to junit

[cssjessica]

Description of Changes

The following spock groovy test were converted to Junit: PointStreamSpec and Nc4IospSpec from Issue https://github.com/Unidata/netcdf-java/issues/1188.

PR Checklist

• [x] Link to any issues that the PR addresses
• [ ] Add labels
• [x] Open as a draft PR until ready for review
• [x] Make sure GitHub tests pass
• [x] Mark PR as "Ready for Review"

[CLAassistant]

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