upgrade rust toolchain to 1.69.0

This brings us closer to the downstream version. Windows link failures
appear with higher versions, this is likely related to rust 1.70 being
the first version to use LLVM 16.

WORKSPACE

@@ -222,8 +222,8 @@ load("@rules_rust//rust:repositories.bzl", "rules_rust_dependencies", "rust_regi
 rules_rust_dependencies()
 
 rust_register_toolchains(
-    edition = "2018",
-    versions = ["1.66.0"],
+    edition = "2021",
+    versions = ["1.69.0"],
 )
 
 load("@rules_rust//crate_universe:repositories.bzl", "crate_universe_dependencies")