fix(deps): update rust crate flipt to v1.4.0

Author: renovate[bot]

crates/flipt/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2024"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-flipt = "=1.1.1"
+flipt = "=1.4.0"
 open-feature = "0.2.7"
 serde_json = "1.0"
 # FIXME: openfeature-rust-sdk-contrib should export this