fix(login): Error handling when failed to prepare for an expired flow

[sawadashota]

Related issue(s)

Fix error handling when failed to prepare for an expired flow.
This may not be happened normally so I don't know how to reproduce this.
But if this error occurs once, kratos logs same error endlessly and resources will be exhaust.

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 green light (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 #2120 (b65a67b) into master (4339cbb) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2120      +/-   ##
==========================================
- Coverage   75.15%   75.14%   -0.02%     
==========================================
  Files         293      293              
  Lines       15600    15600              
==========================================
- Hits        11724    11722       -2     
- Misses       3040     3041       +1     
- Partials      836      837       +1     

Impacted Files	Coverage Δ
selfservice/flow/login/error.go	72.88% <0.00%> (ø)
persistence/sql/persister_courier.go	85.00% <0.00%> (-3.34%)	⬇️

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