chore: add unit test for native currency validation

[bergeron]

Description

Adds unit test coverage for #11693

Related issues

Manual testing steps

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I’ve followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.36%. Comparing base (9f29292) to head (ec76374).
Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12234      +/-   ##
==========================================
+ Coverage   55.78%   56.36%   +0.57%     
==========================================
  Files        1786     1786              
  Lines       40362    40390      +28     
  Branches     5054     5063       +9     
==========================================
+ Hits        22516    22764     +248     
+ Misses      16297    16079     -218     
+ Partials     1549     1547       -2     

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[MarioAslau]

LGTM