docs: add martaarbizu as a contributor for code

[allcontributors[bot]]

Adds @martaarbizu as a contributor for code.

This was requested by handwerkerd in this comment

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.55%. Comparing base (0d66342) to head (d2b8948). Report is 44 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1039 +/- ## ======================================= Coverage 89.55% 89.55% ======================================= Files 26 26 Lines 3466 3466 Branches 634 634 ======================================= Hits 3104 3104 Misses 210 210 Partials 152 152 ```

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