Fixes Fido2Configuration.FullyQualifiedOrigins contains a null entry when configured from a configuration section on .NET 7

[ghost]

Fixes #359

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.95%. Comparing base (e3851a7) to head (5e903e3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #360   +/-   ##
=======================================
  Coverage   77.95%   77.95%           
=======================================
  Files          88       88           
  Lines        2513     2513           
  Branches      421      421           
=======================================
  Hits         1959     1959           
  Misses        439      439           
  Partials      115      115           

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[abergs]

Thank you @ypoul, looks good!

[abergs]

Note for the record: This is changing the public API, but not in a breaking way so can be included without major version bump.