Raise cxxbridge-cmd requires Rust version to 1.70

Author: dtolnay

gen/cmd/Cargo.toml

@@ -10,7 +10,7 @@ homepage = "https://cxx.rs"
 keywords = ["ffi"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/cxx"
-rust-version = "1.56"
+rust-version = "1.70"
 
 [[bin]]
 name = "cxxbridge"