Update bindgen requirement from 0.56.0 to 0.57.0

Updates the requirements on [bindgen](https://github.com/rust-lang/rust-bindgen) to permit the latest version.
- [Release notes](https://github.com/rust-lang/rust-bindgen/releases)
- [Changelog](https://github.com/rust-lang/rust-bindgen/blob/master/CHANGELOG.md)
- [Commits](rust-lang/rust-bindgen@v0.56.0...v0.57.0)

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

Author: dependabot[bot]

gdnative-sys/Cargo.toml

@@ -15,7 +15,7 @@ edition = "2018"
 libc = "0.2"
 
 [build-dependencies]
-bindgen = { version = "0.56.0", default-features = false, features = ["runtime"] }
+bindgen = { version = "0.57.0", default-features = false, features = ["runtime"] }
 proc-macro2 = "1.0.6"
 quote = "1.0.2"
 miniserde = "=0.1.13"