Update rustc_version requirement from ~0.3 to ~0.4

Updates the requirements on [rustc_version](https://github.com/Kimundi/rustc-version-rs) to permit the latest version.
- [Release notes](https://github.com/Kimundi/rustc-version-rs/releases)
- [Commits](https://github.com/Kimundi/rustc-version-rs/compare/v0.3.0...v0.4.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Cargo.toml

@@ -27,7 +27,7 @@ syncable = ["mentat_tolstoy", "tolstoy_traits", "mentat_db/syncable"]
 members = ["tools/cli", "ffi"]
 
 [build-dependencies]
-rustc_version = "~0.3"
+rustc_version = "~0.4"
 
 [dev-dependencies]
 assert_approx_eq = "~1.1"