Compare username based on ID strategy on token refresh

[eva-mueller-coremedia]

When using the option to refresh the token, the expected username and the username from the token might differ in their case.

This lead to an "Username was not the same after refresh". To take the User ID strategy into account, one can use User.idStrategy().equals instead of a plain equals comparison.

Fixes: #392

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 71.88%. Comparing base (791ef3c) to head (a5a97f8).
Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
...va/org/jenkinsci/plugins/oic/OicSecurityRealm.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #394      +/-   ##
============================================
- Coverage     72.47%   71.88%   -0.60%     
+ Complexity      244      239       -5     
============================================
  Files            12       12              
  Lines          1021     1010      -11     
  Branches        148      145       -3     
============================================
- Hits            740      726      -14     
- Misses          201      206       +5     
+ Partials         80       78       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.