Release shotover 0.3.1 (fix)

[rukai]

We failed to properly release both 0.3.0 and 0.3.1 and completely failed to notice.
This is definitely pushing forward a move to https://github.com/axodotdev/cargo-dist for me.

This PR fixes the release.
I'll retag this commit as the true 0.3.1.

[github-actions]

0 benchmark regressed. 1 benchmark improved. Please check the benchmark workflow logs for full details: https://github.com/shotover/shotover-proxy/actions/runs/7878180111

Found 22 outliers among 100 measurements (22.00%)
  12 (12.00%) low severe
  10 (10.00%) low mild
kafka_codec/encode_request_metadata
                        time:   [347.66 ns 352.00 ns 357.46 ns]
                        change: [-27.238% -24.589% -21.804%] (p = 0.00 < 0.05)
                        Performance has improved.