Ensure `ethrex` can be built with locked dependencies on each release

[MegaRedHand]

Locking dependencies is important to avoid built-from-source binaries behaving differently from the pre-built binaries we make for each release. Trying to build ethrex using --locked in the latest releases gives the following error:

$ cargo build --bin ethrex --release --locked --features dev
error: the lock file /Users/mega/ethrex/Cargo.lock needs to be updated but --locked was passed to prevent this
If you want to try to generate the lock file without accessing the network, remove the --locked flag and use --offline instead.

To reproduce:

git clone --branch v0.0.1-rc.1 --depth 1 https://github.com/lambdaclass/ethrex.git
cd ethrex
cargo build --bin ethrex --release --locked --features dev

Note that this doesn't happen when building through cargo install