datetime in Task doesn't match datetime in .task file

Please take a look at [#345](https://github.com/vit-project/vit/issues/345) . I would like to use vit inside a docker container. Unfortunately, the datetimes in Task objects do not necessarily match the true datetimes of tasks. To reproduce the issue, take the following steps:
1. Run `set-up-container.sh` (See the linked issue).
2. Once inside the container, run `generate-dummy-install.sh` and run the export commands that it tells you to.
3. Add `debug.console(task._data)` directly above line 233 of `./usr/lib/python3/dist-packages/vit/task_list.py` and `import vit.debug as debug` to the top of that file.
4. Modify task 2 to have due date `2023-09-13 17:00:00`.
5. Inspect the logs.