build: use minor version for polars upper version bound

[dkrako]

this way dependabot will notify us earlier about deprecations / breaking changes introduced by a new polars release.

[codecov[bot]]

Codecov Report

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

Comparison is base (3ab7e3e) 100.00% compared to head (7792d8b) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #621 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 53 53 Lines 2376 2376 Branches 597 597 ========================================= Hits 2376 2376 ```

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