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-parser/tests/test_parser.rs

@@ -1595,8 +1595,8 @@ mod input_types {
         for input in inputs {
             let (block, err) = parse(&mut working_set, None, input.as_bytes(), true, &[]);
 
-            assert!(err.is_none(), "testing: {}", input);
-            assert_eq!(block.len(), 2, "testing: {}", input);
+            assert!(err.is_none(), "testing: {input}");
+            assert_eq!(block.len(), 2, "testing: {input}");
         }
     }