Bug#993967: License incompatible with current Qt

[Bastian Germann]

Package: tortoisehg
Severity: serious

At https://groups.google.com/g/thg-dev/c/AYFxHk5aLKg/ I started a conversation about TortoiseHg 
(GPLv2-only) having an incompatible license with the currently packaged PyQt5 version (GPLv3). In 
almost a year, upstream did not do anything to handle the issue, so I file this bug. It should be 
possible to convert the source to PySide2 or QtPy (handles PyQt and PySide versions).