Attempting to return pathlib.Path objects in file_dep for a task used as calc_dep of another task ended up failing (exit with return code 3).

I assume this is because of how doit uses saved values to pass the result of the original task. This behaviour, is not explicit in documentation, and for some reason (still under investigation, likely related to our custom reporter), there were no explicit errors except the non-zero exit code when we ran this in our project (scality/metalk8s). Trying to provide a minimal reproducing example led me to understand the issue came from the values returned in the calc_dep task (see gdemonet/doit-calc-deps-issue#1).