chore(deps): Update config to 0.15.8 (atuinsh#2580)

This fixes a panic when non-Unicode environment variables are
processed by atuin.

Author: Jongy

Cargo.lock

@@ -23,7 +23,7 @@ time = { version = "0.3.36", features = [
   "local-offset",
 ] }
 clap = { version = "4.5.7", features = ["derive"] }
-config = { version = "0.13", default-features = false, features = ["toml"] }
+config = { version = "0.15.8", default-features = false, features = ["toml"] }
 directories = "5.0.1"
 eyre = "0.6"
 fs-err = "2.9"