Use variable names directly in the format strings (#7906)

# Description

Lint: `clippy::uninlined_format_args`

More readable in most situations.
(May be slightly confusing for modifier format strings
https://doc.rust-lang.org/std/fmt/index.html#formatting-parameters)

Alternative to #7865

# User-Facing Changes

None intended

# Tests + Formatting

(Ran `cargo +stable clippy --fix --workspace -- -A clippy::all -D
clippy::uninlined_format_args` to achieve this. Depends on Rust `1.67`)

tests/shell/pipeline/commands/external.rs

@@ -309,8 +309,8 @@ mod external_words {
             let actual = nu!(
                 cwd: dirs.test(), pipeline(
                 &format!(r#"
-                    nu --testbin meow {} | from toml | get nu_party_venue
-                "#, nu_path_argument)
+                    nu --testbin meow {nu_path_argument} | from toml | get nu_party_venue
+                "#)
             ));
 
             assert_eq!(actual.out, "zion");