fix: account linking should only happen after 2fa when required

[zepatrik]

Currently account linking happens after the first factor, even when the second factor is required for a session to be issued.

[codecov]

Codecov Report

Attention: Patch coverage is 83.82353% with 11 lines in your changes missing coverage. Please review.

Project coverage is 78.58%. Comparing base (b4c453b) to head (27d96ba).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
selfservice/flow/settings/handler.go	85.29%	5 Missing ⚠️
selfservice/flow/login/hook.go	85.71%	1 Missing and 3 partials ⚠️
session/manager_http.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4174      +/-   ##
==========================================
+ Coverage   78.57%   78.58%   +0.01%     
==========================================
  Files         379      379              
  Lines       27042    27052      +10     
==========================================
+ Hits        21249    21260      +11     
  Misses       4181     4181              
+ Partials     1612     1611       -1     

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[hperl]

Very nice!