docs: iban might be invalid due to country specific rules

[ST-DDT]

Addresses #1832

• finance.iban does not create valid iban #1832

This PR adds a more specific warning to the IBAN method to make it more obvious that it randomly generates the IBAN without taking country specific rules into account.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.96%. Comparing base (df59724) to head (4c9311d).
Report is 1 commits behind head on next.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #3175      +/-   ##
==========================================
- Coverage   99.96%   99.96%   -0.01%     
==========================================
  Files        2798     2798              
  Lines      227367   227367              
  Branches      578      576       -2     
==========================================
- Hits       227292   227280      -12     
- Misses         75       87      +12     

Files with missing lines	Coverage Δ
src/modules/finance/index.ts	100.00% <ø> (ø)

... and 2 files with indirect coverage changes