fix: distinguish credential types properly when collecting identifiers

[zepatrik]

closes #2872

[codecov]

Codecov Report

Merging #2873 (ea4571b) into master (9eeedc0) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2873      +/-   ##
==========================================
+ Coverage   75.92%   76.01%   +0.08%     
==========================================
  Files         303      303              
  Lines       18249    18251       +2     
==========================================
+ Hits        13856    13873      +17     
+ Misses       3326     3314      -12     
+ Partials     1067     1064       -3     

Impacted Files	Coverage Δ
identity/extension_credentials.go	100.00% <100.00%> (ø)
persistence/sql/persister_courier.go	86.86% <0.00%> (+4.04%)	⬆️
courier/courier_dispatcher.go	72.88% <0.00%> (+18.64%)	⬆️

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