fix: fixed error handling in persister

[mitar]

Checklist

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• 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.
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• I have added tests that prove my fix is effective or that my feature
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[mitar]

I also noticed duplicated code, so I removed that.

[aeneasr]

Thank you! Looking good, just a minor change

[codecov]

Codecov Report

Merging #2860 (6e0c693) into master (f15f339) will decrease coverage by 0.05%.
The diff coverage is 61.53%.

@@            Coverage Diff             @@
##           master    #2860      +/-   ##
==========================================
- Coverage   49.87%   49.82%   -0.06%     
==========================================
  Files         236      236              
  Lines       14974    14958      -16     
==========================================
- Hits         7469     7453      -16     
  Misses       6843     6843              
  Partials      662      662              

Impacted Files	Coverage Δ
persistence/sql/persister_oauth2.go	81.70% <61.53%> (-1.17%)	⬇️

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[aeneasr]

🙏