10542: Use workspace cargo to fetch rust source's metadata r=lnicola a=Alexendoo
Previously the detected cargo is the global one, as it uses the
directory of the rust source which doesn't pick up the local override
This fixes the case in clippy where the local rust toolchain is a recent
nightly that has a 2021 edition Cargo.toml. The global (stable) cargo
returns an error attempting to parse it
Fixes#10445
Co-authored-by: Alex Macleod <alex@macleod.io>
3c468ab2fc