Update prost requirement from 0.11.8 to 0.12.1

Updates the requirements on [prost](https://github.com/tokio-rs/prost) to permit the latest version.
- [Release notes](https://github.com/tokio-rs/prost/releases)
- [Commits](tokio-rs/prost@v0.11.8...v0.12.1)

---
updated-dependencies:
- dependency-name: prost
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

save/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-prost = "0.11.8"
+prost = "0.12.1"
 redb = "1.0"
 thiserror = "1.0.38"
 zstd = { package = "zstd-safe", version = "6.0.4", features = ["std", "experimental"] }