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`)

crates/nu-cli/src/prompt_update.rs

@@ -106,8 +106,7 @@ pub(crate) fn update_prompt<'prompt>(
     let left_prompt_string = if config.shell_integration {
         if let Some(prompt_string) = left_prompt_string {
             Some(format!(
-                "{}{}{}",
-                PRE_PROMPT_MARKER, prompt_string, POST_PROMPT_MARKER
+                "{PRE_PROMPT_MARKER}{prompt_string}{POST_PROMPT_MARKER}"
             ))
         } else {
             left_prompt_string