Fix cohort.get_sequencing_groups in cpg_workflows targets.py

[EddieLF]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 64.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 77.39%. Comparing base (3d7b16c) to head (9bebd60).

Files with missing lines	Patch %	Lines
cpg_workflows/targets.py	60.86%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #899      +/-   ##
==========================================
- Coverage   78.50%   77.39%   -1.12%     
==========================================
  Files          10       10              
  Lines        1791     1809      +18     
==========================================
- Hits         1406     1400       -6     
- Misses        385      409      +24     

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[MattWellie]

I think this is also close-able WRT #959, which guts all crossover between Cohorts and Datasets