`[patch.crates-io]` with local crate fails

Patching the `simple-workspace` example to [replace a crates dependency with an local crate](https://github.com/yusdacra/nix-cargo-integration/commit/5c4ba224ed5388a9337e3a840eb8f76b26c73ff1) leads to problems when building the dependencies.

Content of the build directory:
```
nix-build-my-crate-deps-0.1.0.drv-0
├── env-vars
├── nix-vendor
│ ├── hermit-abi-0.3.9
│ │ ├── ...
│ └── num_cpus-1.16.0 # has dependency to libc
│ ├── ...
└── simple-workspace
├── Cargo.lock
├── Cargo.toml
├── libc # is found by nix but is empty
│ ├── Cargo.toml
│ └── src
│ ├── bin # dummy main.rs
│ └── lib.rs # dummy
├── my-crate
│ ├── ...
├── my-other-crate
│ ├── ...
└── target
├── ...
```

Is there any way to fix the dependency chain? Excluding the crate from the workspace does not change anything, it still seems to show up as empty in the `simple-workspace` directory instead of the `nix-vendor` directory.