chore: Fix broken coverage script

[FrederikBolding]

Our coverage script would overwrite the current values with the new ones and thus never report increases.

---

Note

Fixes a mutation bug in the coverage update script and updates coverage.json with increased branches/functions percentages.

• Scripts:
  • Fix mutation bug in scripts/update-coverage.mts by initializing reducer with percentages: { ...currentCoverage } to prevent overwriting values.
• Coverage:
  • Update packages/snaps-controllers/coverage.json with increased branches and functions percentages.

^{Written by Cursor Bugbot for commit d2f60cd. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.30%. Comparing base (3c846f0) to head (d2f60cd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3657   +/-   ##
=======================================
  Coverage   98.30%   98.30%           
=======================================
  Files         417      417           
  Lines       11927    11927           
  Branches     1844     1844           
=======================================
  Hits        11725    11725           
  Misses        202      202           

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