CSUB-619: Add more tests for register_address_v2

[zacharyfrederick]

Description of proposed changes

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Practical tips for PR review & merge:

• All GitHub Actions report PASS
• Newly added code/functions have unit tests
  • Coverage tools report all newly added lines as covered
  • The positive scenario is exercised
  • Negative scenarios are exercised, e.g. assert on all possible errors
  • Assert on events triggered if applicable
  • Assert on changes made to storage if applicable
• Modified behavior/functions - try to make sure above test items are covered
• Integration tests are added if applicable/needed

[codecov-commenter]

Codecov Report

Merging #1202 (daeb5b9) into dev (4beef4e) will decrease coverage by 0.07%.
The diff coverage is 61.85%.

@@            Coverage Diff             @@
##              dev    #1202      +/-   ##
==========================================
- Coverage   69.57%   69.50%   -0.07%     
==========================================
  Files         100      100              
  Lines       11791    11877      +86     
  Branches       89       89              
==========================================
+ Hits         8203     8255      +52     
- Misses       3588     3622      +34     

Impacted Files	Coverage Δ
pallets/creditcoin/src/tests.rs	98.16% <57.83%> (-1.69%)	⬇️
pallets/creditcoin/src/helpers.rs	83.18% <75.00%> (-0.93%)	⬇️
pallets/creditcoin/src/lib.rs	83.69% <100.00%> (+0.23%)	⬆️

... and 1 file with indirect coverage changes

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[github-actions]

For full LLVM coverage report click here!

[atodorov]

Some minor changes requested.