fix: registration code ui nodes group

[Benehiko]

The registration with code method incorrectly returns UI nodes for traits on group code. When only the code method is enabled, this wouldn't cause a problem in the UI, however, with multiple methods enabled which per default use the default group to map methods to the UI, this becomes a problem, since the UI would map duplicate nodes.

Although this could be changed in the UI consuming the API and would not cause any data submit problems, Kratos should rather stay consistent with using the default group with traits on login and registration flows.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Merging #3505 (01e6e27) into master (57a3273) will increase coverage by 0.00%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

❗ Current head 01e6e27 differs from pull request most recent head 2dc12bd. Consider uploading reports for the commit 2dc12bd to get more accurate results

@@           Coverage Diff           @@
##           master    #3505   +/-   ##
=======================================
  Coverage   78.37%   78.38%           
=======================================
  Files         339      340    +1     
  Lines       22492    22518   +26     
=======================================
+ Hits        17628    17650   +22     
- Misses       3556     3561    +5     
+ Partials     1308     1307    -1     

Files Changed	Coverage Δ
selfservice/strategy/code/strategy.go	80.80% <100.00%> (ø)

... and 2 files with indirect coverage changes