Replace references to .cargo/config with .cargo/config.toml

[TwelfthGhast]

warning: `~/.cargo/config` is deprecated in favor of `config.toml`
note: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`

Using:

cargo 1.79.0 (ffa9cf99a 2024-06-03)
rustc 1.79.0 (129f3b996 2024-06-10)