TASKBIN env var for taskwarrior task executable.

Hi.

I've experienced a name clash between task (taskwarrior executable) and task (form task runner from go-task in go).

Ideally, I would appreciate if the taskwarrior executable could be fed to tasksh using a TASKBIN environment variable. That would allow me to perform a clean resolution of that name clash.

(Otherwise, there are aliases and a whole lot of nonsense that I'd rather not go to if possible).

References:

https://github.com/GothenburgBitFactory/taskwarrior/issues/3463
https://github.com/go-task/task/issues/1672
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1071939