Cargo commands are affected by the `.cargo/config` files above
their working directory. If cargo is invoked from above the directory
holding `Cargo.toml`, it may not pick up important settings like
registry replacements, causing it to behave differently or even fail.
Most cargo invocations are currently setting their working directories
to the directory containing `Cargo.toml`, but a couple of paths remain
in which cargo is invoked from the default workspace root instead.
This change fixes that, resolving some cargo check failures that I
experienced in a multi-root workspace in which packages used different
registries.
c4664609ed