AssertionError in test_git_dirty_notag in UTC-N after N before midnight

When I run tests on master, I get a failure in `test_git`:

```
FAILED testing/test_git.py::test_git_dirty_notag - AssertionError: assert '.d20200506' in '0.1.dev1+ge5adfd7.d20200507'
```

It's currently May 6 where I am but May 7 in UTC.

I suspect the issue is that git is generating dates in UTC but the tests are using a local date.