Update to rustix 0.36.

This is a minor update; the main change is that it uses io-lifetimes
1.0 internally, which means that on Rust 1.64 and later it's using the
`OwnedFd` etc. from std instead of its own. This is not exposed in
memfd's public API.

Cargo.toml

@@ -16,7 +16,7 @@ exclude = [".gitignore", ".travis.yml"]
 
 [dependencies]
 # Private dependencies.
-rustix = { version = "0.35.6", features = ["fs"] }
+rustix = { version = "0.36.0", features = ["fs"] }
 
 [package.metadata.release]
 disable-publish = true