dnsdist: Fix release builds by updating the locked Rust lib version

dnsdist: Fix release builds by updating the locked Rust lib version

Since we are now dynamically setting the version of our internal Rust library
when generating the release tarball, `cargo` needs to update the `Cargo.lock`
file to reflect the new version, which is not possible if we are passing `--locked`:
```
error: the lock file /pdns/dnsdist-2.1.0-alpha0.870.master.gc64b979bc/dnsdist-rust-lib/rust/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.
```
This commit fixes that also updating the `Cargo.lock` file when generating the
release tarball so that `cargo` no longer needs to update the `Cargo.lock`.

Signed-off-by: Remi Gacogne <remi.gacogne@powerdns.com>