itest: work around clippy errors when quote! generates one big line

[Yarwin]

add #[allow(clippy::suspicious_else_formatting)] in generated code in itest, since file can be generated as one big line.

See failing job: https://github.com/godot-rust/gdext/actions/runs/18001547399/job/51211796501?pr=1334

As explanation, such code:

    if a {
        println!("a");
        godot_error = true;
    }
    if b {
        println!("b");
        godot_error = true;
    }

is fine, while

    if a {
        println!("a");
        godot_error = true;
    } if b {
        println!("b");
        godot_error = true;
    }

triggers following warning:

warning: this looks like an `else if` but the `else` is missing
 --> src/main.rs:6:6
  |
6 |     } if b {
  |      ^
  |
  = note: to remove this lint, add the missing `else` or add a new line before the second `if`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#suspicious_else_formatting
  = note: `#[warn(clippy::suspicious_else_formatting)]` on by default

[GodotRust]

API docs are being generated and will be shortly available at: https://godot-rust.github.io/docs/gdext/pr-1336

[Bromeon]

Thanks!