Fixes memory leak in `frequentist_stats._resample_and_agg_once`

[codecov-commenter]

Codecov Report

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

Comparison is base (20c13ee) 76.18% compared to head (e3172e5) 76.22%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #195 +/- ## ========================================== + Coverage 76.18% 76.22% +0.04% ========================================== Files 23 23 Lines 974 976 +2 ========================================== + Hits 742 744 +2 Misses 232 232 ``` | [Flag](https://app.codecov.io/gh/mozilla/mozanalysis/pull/195/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | Coverage Δ | | |---|---|---| | [py38](https://app.codecov.io/gh/mozilla/mozanalysis/pull/195/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | `76.22% <100.00%> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/mozilla/mozanalysis/pull/195?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | Coverage Δ | | |---|---|---| | [src/mozanalysis/frequentist\_stats/bootstrap.py](https://app.codecov.io/gh/mozilla/mozanalysis/pull/195?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21vemFuYWx5c2lzL2ZyZXF1ZW50aXN0X3N0YXRzL2Jvb3RzdHJhcC5weQ==) | `94.44% <100.00%> (+0.32%)` | :arrow_up: |

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