Temporary test directories not removed

[dennisvang]

https://github.com/Digital-Sapphire/PyUpdater/blob/282760de71ea6501b90d90d85b5fc6ad1d0c2bd8/tests/conftest.py#L45-L47

From tempfile docs:

The user of mkdtemp() is responsible for deleting the temporary directory and its contents when done with it.

On Windows 10, running the tests leaves AppData\Local\Temp full of empty "tmp*" directories.