Fix SSO config removal in quilt3.admin.sso_config.set()

[sir-sigurd]

Description

TODO

• Unit tests
• Changelog entry (skip if change is not significant to end users, e.g. docs only)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 38.47%. Comparing base (4f81266) to head (33c4dd2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #4098    +/-   ##
========================================
  Coverage   38.47%   38.47%            
========================================
  Files         723      723            
  Lines       33218    33219     +1     
  Branches     4879     4879            
========================================
+ Hits        12781    12782     +1     
+ Misses      19813    19289   -524     
- Partials      624     1148   +524     

Flag	Coverage Δ
api-python	90.85% <100.00%> (+<0.01%)	⬆️
catalog	11.45% <ø> (ø)
lambda	87.97% <ø> (ø)

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