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-term-grid/examples/grid_demo.rs

@@ -23,7 +23,7 @@ fn main() {
     }
 
     if let Some(grid_display) = grid.fit_into_width(80) {
-        println!("{}", grid_display);
+        println!("{grid_display}");
     } else {
         println!("Couldn't fit grid into 80 columns!");
     }