Fix cohort.get_sequencing_groups in cpg_workflows targets.py

[EddieLF]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 51.85185% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.45%. Comparing base (3d7b16c) to head (419b10d).
⚠️ Report is 376 commits behind head on main.

Files with missing lines	Patch %	Lines
cpg_workflows/targets.py	50.00%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #899       +/-   ##
===========================================
- Coverage   78.50%   53.45%   -25.06%     
===========================================
  Files          10       10               
  Lines        1791     1811       +20     
===========================================
- Hits         1406      968      -438     
- Misses        385      843      +458     

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[MattWellie]

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