Update examles/rust/msm dockerfile to fix bug

[cyl19970726]

Describe the changes

There is a conflict between https://github.com/ingonyama-zk/icicle/blob/main/examples/rust/msm/Cargo.toml#L7 and https://github.com/ingonyama-zk/icicle/blob/main/examples/rust/msm/.devcontainer/Dockerfile#L24, it leads to an error happen when executing cargo run --release at docker

[jeremyfelder]

@cyl19970726 Thanks for your contribution! 🚀

What docker command are you running with this?

I think this will still produce an error if the context of the docker build is the examples/rust/msm directory since the COPY command won't be able to access outside the context