Update bindgen requirement from 0.70.1 to 0.71.0 (#37)

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/main/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/rust-bindgen/commits)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

creachadair-imath-sys/Cargo.toml

@@ -16,7 +16,7 @@ include = ["src/*", "vendor/imath/*.{c,h}", "Cargo.toml", "build.rs", "tests/"]
 
 [build-dependencies]
 cc = "1.0.67"
-bindgen = { version = "0.70.1", default-features = false, features = [
+bindgen = { version = "0.71.0", default-features = false, features = [
   "runtime",
 ] }
 dunce = "1.0.1"