bf: yaml should be optional

[asmacdo]

Fixes: #245

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 93.64%. Comparing base (5c77ff9) to head (31d115a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/con_duct/suite/ls.py	50.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #248      +/-   ##
==========================================
- Coverage   94.12%   93.64%   -0.49%     
==========================================
  Files           5        5              
  Lines         749      755       +6     
  Branches       95       96       +1     
==========================================
+ Hits          705      707       +2     
- Misses         26       29       +3     
- Partials       18       19       +1     

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