build: update bundler in Ruby tests

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #345 will not alter performance

_{:warning: No base runs were found}

_{Falling back to comparing dd/fix-ruby (cc60721) with master (ee8a49e)}

Summary

✅ 6 untouched benchmarks

[codecov[bot]]

Codecov Report

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

Project coverage is 85.04%. Comparing base (fe73893) to head (cc60721).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #345 +/- ## ======================================= Coverage 85.04% 85.04% ======================================= Files 18 18 Lines 1759 1759 ======================================= Hits 1496 1496 Misses 263 263 ```

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