fix: don't show oidc subject in login hints

[jonas-jonas]

In some configurations, if the identity only has an OIDC credential, the login hint message would contain an OIDC identifier including the subject, which is useless to the user.

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
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  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

Attention: Patch coverage is 55.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 78.59%. Comparing base (23f3232) to head (baa077f).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
identity/manager.go	52.63%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4264      +/-   ##
==========================================
- Coverage   78.61%   78.59%   -0.03%     
==========================================
  Files         381      381              
  Lines       27385    27376       -9     
==========================================
- Hits        21528    21515      -13     
- Misses       4237     4239       +2     
- Partials     1620     1622       +2     

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