Revert "chore: Bump Rust version to 1.77 (#9631)" (#9658)

This reverts commit cdd1be672d.

We can't upgrade to Rust 1.77 until there are Rust 1.77 Docker images
available
(https://github.com/docker-library/official-images/pull/16457).


Release Notes:

- N/A

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
-channel = "1.77"
+channel = "1.76"
 profile = "minimal"
 components = [ "rustfmt", "clippy" ]
 targets = [ "x86_64-apple-darwin", "aarch64-apple-darwin", "x86_64-unknown-linux-gnu", "wasm32-wasi" ]