Bump the version of virtualenv in tox.ini to pull in the correct version of pip

[codecov[bot]]

Codecov Report

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

Project coverage is 83.76%. Comparing base (a8fd59d) to head (df61976).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #125 +/- ## ======================================= Coverage 83.76% 83.76% ======================================= Files 34 34 Lines 3413 3413 ======================================= Hits 2859 2859 Misses 554 554 ``` | [Flag](https://app.codecov.io/gh/fox-it/flow.record/pull/125/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fox-it) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/fox-it/flow.record/pull/125/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fox-it) | `83.76% <ø> (ø)` | | 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=fox-it#carryforward-flags-in-the-pull-request-comment) to find out more.

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