Turn off conda initialization during incremental compilation?

If you have a `using PythonCall` inside your package "Foo", then just _precompiling_ Foo will trigger creation of the PythonCall's Conda environment, downloading of packages, etc...

IMO this is undesired. I know there's environment variables to prevent this, but while I remember to set them when actually running a program, its very often I forget during precompilation, especially since precompilation automatically gets triggered at various times (when instantiating, upgrading, etc...)

Wondering if it makes sense to turn that off during precompilation entirely with a check to `ccall(:jl_generating_output, Cint, ())`? It would mean Python wouldn't be available to any dependent packages during precompilation either, but perhaps thats a better behavior? I don't have the strongest feelings one way or the either, probably leaning slightly that it'd be nicer to make this change, but just wanted to point out.