Reproducer for a nix cargoLock bug

these 2 derivations will be built:
  /nix/store/z8v8wc2rkbbi9sdijf1yjiw6lh7cz100-cargo-vendor-dir.drv
  /nix/store/jkwqs9zd1x78d2i19dqydq8nr4mg9brf-gitlockreproducer.drv
building '/nix/store/z8v8wc2rkbbi9sdijf1yjiw6lh7cz100-cargo-vendor-dir.drv'...
building '/nix/store/jkwqs9zd1x78d2i19dqydq8nr4mg9brf-gitlockreproducer.drv'...
Running phase: unpackPhase
unpacking source archive /nix/store/513bb2xfxhy7ysdgf9vq5n9xwy99bc0a-cargoimport
source root is cargoimport
Executing cargoSetupPostUnpackHook
Finished cargoSetupPostUnpackHook
Running phase: patchPhase
Executing cargoSetupPostPatchHook
Validating consistency between /build/cargoimport/Cargo.lock and /build/cargo-vendor-dir/Cargo.lock
Finished cargoSetupPostPatchHook
Running phase: updateAutotoolsGnuConfigScriptsPhase
Running phase: configurePhase
Running phase: buildPhase
Executing cargoBuildHook
cargoBuildHook flags: -j 16 --target x86_64-unknown-linux-gnu --offline --profile release
error: failed to load source for dependency `async-signature`

Caused by:
  Unable to update https://github.com/baloo/traits.git?branch=baloo%2Fasync-signature%2Fprehash-signer#7eec720f

Caused by:
  can't checkout from 'https://github.com/baloo/traits.git': you are in the offline mode (--offline)