Fit service name for sso-admin

[giograno]

This small PR fixes the service name passed to the BackendDict for the SSO Admin service.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.33%. Comparing base (f4eaa87) to head (e3cfdcc).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7717   +/-   ##
=======================================
  Coverage   94.33%   94.33%           
=======================================
  Files        1087     1087           
  Lines       92858    92858           
=======================================
  Hits        87598    87598           
  Misses       5260     5260           

Flag	Coverage Δ
servertests	29.48% <100.00%> (ø)
unittests	94.30% <100.00%> (ø)

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[github-actions[bot]]

This is now part of moto >= 5.0.8.dev21