Git submodules using `git` urls can break `cargo install`

[Hoverbear]

Currently if a user attempts to install youki via Cargo, they may meet an error if they do not have git keys configured fully:

❯ cargo install --git https://github.com/containers/youki
    Updating git repository `https://github.com/containers/youki`
    Updating git submodule `[email protected]:opencontainers/runtime-tools.git`
error: failed to update submodule `integration_tests/oci-runtime-tests`

Caused by:
  failed to fetch submodule `integration_tests/oci-runtime-tests` from [email protected]:opencontainers/runtime-tools.git

Caused by:
  failed to authenticate when downloading repository

  * attempted ssh-agent authentication, but no usernames succeeded: `git`

  if the git CLI succeeds then `net.git-fetch-with-cli` may help here
  https://doc.rust-lang.org/cargo/reference/config.html#netgit-fetch-with-cli

It may be desirable to use a different Git submodule remote URL protocol.

While attempting to build youki in a sandbox without configured git keys I notably saw this error which I think might be related?:

youki>    Compiling futures-executor v0.3.24
youki>    Compiling futures v0.3.24
youki> error: failed to run custom build command for `youki v0.0.3 (/build/source/crates/youki)`
youki> Caused by:
youki>   process didn't exit successfully: `/build/source/target/release/build/youki-e2aad9c6a21f0e82/build-script-build` (exit status: 1)
youki>   --- stderr
youki>   Error: could not find repository from '/build/source/crates/youki'; class=Repository (6); code=NotFound (-3)
youki> warning: build failed, waiting for other jobs to finish...
error: builder for '/nix/store/4769q3a9n0d3ay1qmbha0q5brvg9jv6q-youki-0.0.3.drv' failed with exit code 101;
       last 10 log lines:
       >    Compiling youki v0.0.3 (/build/source/crates/youki)
       >    Compiling futures-executor v0.3.24
       >    Compiling futures v0.3.24
       > error: failed to run custom build command for `youki v0.0.3 (/build/source/crates/youki)`
       >
       > Caused by:
       >   process didn't exit successfully: `/build/source/target/release/build/youki-e2aad9c6a21f0e82/build-script-build` (exit status: 1)
       >   --- stderr
       >   Error: could not find repository from '/build/source/crates/youki'; class=Repository (6); code=NotFound (-3)
       > warning: build failed, waiting for other jobs to finish...
       For full logs, run 'nix log /nix/store/4769q3a9n0d3ay1qmbha0q5brvg9jv6q-youki-0.0.3.drv'.