Remove invoke-related monkeypatch in tasks.py

[kotfu]

Python 3 deprecated inspect.getargspec. Python 3.11 removed it. The invoke package is not very well maintained and still requires inspect.getargspec. The first PR to fix this issue, pyinvoke/invoke#458, was created in 2017. Another one was created in 2019: pyinvoke/invoke#606.

If these don't get fixed soon, we'll have to abandon invoke and go with (or build) something better.