fix: sync filter_mod.dopplerfold with filter_mod

[hkershaw-brown]

Description:

filter_mod.dopplerfold.f90 out of sync with filter (missing the latest QC bug fix https://github.com/NCAR/DART/pull/450

Fixes issue

fixes: #565

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.

I don't believe there is documentation for filter_dopplerfold at the moment. It is a hidden feature.

Tests

Please describe any tests you ran to verify your changes.

Compiled wrf with filter_mod.dopplerfold.f90

cd DART/wrf/work
cp ../../../assimilation_code/modules/assimilation/filter_mod.dopplerfold.f90 filter_mod.f90
./quickbuild.sh 

Checklist for merging

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

Checklist for release

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

Testing Datasets

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