Edit cam-fv assimilate.csh.template to improve purge logic for restarts

[johnsonbk]

Description:

This modification of the assimilate.csh.template for cam-fv fixes the issue in which restart files sometimes aren't being purged when the interval between restart saves is a string rather than an integer.

Fixes issue

fixes #435

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update

Documentation changes needed?

• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.

Tests

Set up a FHIST run on the f09_g17 grid and cycled for two weeks to ensure that this change fixes the issue.

Checklist for merging

• [x] Updated changelog entry
• [ ] Documentation updated
• [x] Update conf.py

Checklist for release

• [x] Merge into main
• [x] Create release from the main branch with appropriate tag
• [x] Delete feature-branch

Testing Datasets

• [ ] Dataset needed for testing available upon request
• [ ] Dataset download instructions included
• [ ] No dataset needed

[hkershaw-brown]

@hkershaw-brown bundle with #425