Add Cargo.lock to git tracking

[GuillaumeGomez]

To prevent unexpected MSRV bumps and have a better tracking of dependencies.

[GuillaumeGomez]

error[duplicate]: found 2 duplicate entries for crate 'toml_edit'
    ┌─ /github/workspace/Cargo.lock:120:1
    │  
120 │ ╭ toml_edit 0.20.7 registry+https://github.com/rust-lang/crates.io-index
121 │ │ toml_edit 0.21.0 registry+https://github.com/rust-lang/crates.io-index
    │ ╰──────────────────────────────────────────────────────────────────────^ lock entries

is coming from proc-macro-crate but we're already using its latest version.

[sdroege]

See bkchr/proc-macro-crate#41 . For now add a ignore for this duplication to deny.toml (add the old version).

[GuillaumeGomez]

All good. :)