Cargo process fails when cargo metadata spits warnings to std-error

[rinconjc]

I have a Rust workspace with 2 children members. When I try to invoke cargo actions from any of the members, it doesn't do anything.
The reasons seems that cargo metada is spitting some warning to the std-error along with the actual json metadata. However, cargo-process--workspace-root concatenates both outputs and tries to json-parse, and hence failing to do so.
The root cause seems that shell-command-to-string combines the std-out/std-error in the response.