Avoid skipping entire tests when pandas is not installed

[codecov[bot]]

Codecov Report

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

Comparison is base (92a7535) 92.41% compared to head (5a545cd) 92.40%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #574 +/- ## ========================================== - Coverage 92.41% 92.40% -0.02% ========================================== Files 28 28 Lines 2941 2937 -4 ========================================== - Hits 2718 2714 -4 Misses 223 223 ```

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