fix(StoreCredit): Add display_number method

[tvdeyen]

Summary

display_number is used by many partials and templates displaying the payment source identifier to users
or admins.

StoreCredit was missing this method, leading to errors if a store credit is used as payment source.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.84%. Comparing base (5b65373) to head (89aaf70).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5741   +/-   ##
=======================================
  Coverage   88.84%   88.84%           
=======================================
  Files         704      704           
  Lines       16764    16765    +1     
=======================================
+ Hits        14894    14895    +1     
  Misses       1870     1870           

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[kennyadsl]

@tvdeyen Approving, but it would be great if you could specify in which scenario and which pages exactly you did see those errors, for future reference. Thanks Thomas!

[tvdeyen]

@tvdeyen Approving, but it would be great if you could specify in which scenario and which pages exactly you did see those errors, for future reference. Thanks Thomas!

@kennyadsl We saw this in our custom invoice pdf template, where we simply loop over all payments and display each payment.source.display_number. We could have solved it with a respond_to(:display_number), but think it is more convenient to be able just call display_number on any source (hence the name, that we probably want to change to something more generic in the future).

[github-actions]

💚 All backports created successfully

Status	Branch	Result
✅	v4.3

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