A patched version of cargo local-registry is required, this can be installed via cargo install --git https://github.com/jarhodes314/cargo-local-registry --branch feature/null-checksums.
This is an example of a maximally simple Rust crate with a git dependency cached in a local registry. Using cargo 1.63.0, running cargo build --frozen will fail, but with the changes in rust-lang/cargo#11188, it will succeed, as cargo will not try and add a checksum field to the "example" dependency. Running cargo local-registry -s Cargo.lock registry --git (to update the local registry) should succeed.
To see the motivation behind omitting the checksum from the registry rather than calculating a fake one in cargo local-registry, modify the registry index for example to contain "cksum":"" instead of "cksum":null. Running cargo build with cargo 1.63.0 will add the checksum field into the lockfile. This will cause cargo local-registry -s Cargo.lock registry --git to fail. This is the primary reason why the change needs to be in cargo, rather than in cargo local-registry.